iMac very slow after High Sierra upgrade (EtreCheck report included)

My iMac become very slow after upgrading to High Sierra a few months back. Even opening Safari with no other app open takes ages, with the colour wheel spinning.

I have run EtreCheck (report pasted below) but it shows no Major Issues, and I couldn't interpret the Minor Issues. It says Performance is "Good".

I have 4MB RAM which isn't a lot, but Activity Monitor always shows green Memory Pressure, and CPU always tends to be idle 90% or more so doesn't seem like a CPU issue. I have done NVPRAM and SMC resets and it makes no difference. I have followed instructions from a number of "10 things to improve your Mac's performance" type articles (out of desperation rather than faith in those articles) but no improvement.

Could it be the SATA drive that needs replacing with a SSD? I have heard that High Sierra is unforgiving on non-SSD drives. The SATA drive always seems to be making a noise and doing something even when I am not using the Mac.

If anyone can look at the EtreCheck report below and have any ideas, that would be really appreciated. Thanks in advance!

EtreCheck version: 4.1 (4A162)

Report generated: 2018-03-03 10:47:54

Download EtreCheck from https://etrecheck.com

Runtime: 4:47

Performance: Good

Problem: Computer is too slow

Major Issues: None

Minor Issues:

These issues do not need immediate attention but they may indicate future problems.

Upgradeable RAM - This machine has upgradeable RAM that would help its performance.

Clean up - There are orphan files that could be removed.

Small backup drive - Time Machine backup drive is too small.

Unsigned files - There is unsigned software installed. It appears to be legitimate but should be reviewed.

Hardware Information:

iMac (27-inch, Mid 2011)

iMac Model: iMac12,2

1 2.7 GHz Intel Core i5 (i5-2500S) CPU: 4-core

4 RAM At maximum

BANK 0/DIMM0

2 GB DDR3 1333 ok

BANK 1/DIMM0

2 GB DDR3 1333 ok

BANK 0/DIMM1

Empty

BANK 1/DIMM1

Empty

Video Information:

Intel HD Graphics 3000 - VRAM: 384 MB

AMD Radeon HD 6770M - VRAM: 512 MB

iMac 2560 x 1440

Drives:

disk0 - WDC WD1001FALS-403AA0 1.00 TB (Mechanical)

Internal SATA 3 Gigabit Serial ATA

disk0s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk0s2 - i******k (Journaled HFS+) 999.35 GB

disk0s3 - Recovery HD [Recovery] 650 MB

disk1 - WD 999.50 GB

External FireWire

disk1s1 32 KB

disk1s3 - i*************p (Journaled HFS+) 999.37 GB

disk2 - WD 2.00 TB

External FireWire

disk2s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk2s2 - E*******************1 (Journaled HFS+) 2.00 TB

disk3 - Western Digital Elements 25A2 2.00 TB

External USB 480 Mbit/s

disk3s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk3s2 - E*******************2 (Journaled HFS+) 2.00 TB

disk4 - Western Digital My Passport 25E4 4.00 TB

External USB 480 Mbit/s

disk4s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk4s2 - E**********k (Journaled HFS+) 4.00 TB

disk5 - SanDisk Cruzer Blade 62.72 GB

External USB 480 Mbit/s

disk5s1 - S******P (MS-DOS FAT32) 62.71 GB

Mounted Volumes:

disk0s2 - i******k 999.35 GB (548.75 GB free)

Journaled HFS+

Mount point: /

disk1s3 - i*************p 999.37 GB (388.14 GB free)

Journaled HFS+

Mount point: /Volumes/i*************p

disk2s2 - E*******************1 2.00 TB (511.73 GB free)

Journaled HFS+

Mount point: /Volumes/E*******************1

disk3s2 - E*******************2 2.00 TB (284.09 GB free)

Journaled HFS+

Mount point: /Volumes/E*******************2

disk4s2 - E**********k 4.00 TB (795.94 GB free)

Journaled HFS+

Mount point: /Volumes/E**********k

disk5s1 - S******P 62.71 GB (46.03 GB free)

MS-DOS FAT32

Mount point: /Volumes/S******P

Network:

Interface en0: Ethernet

One IPv4 address

Interface en6: iPad

Interface en5: iPhone

Interface fw0: FireWire

Interface en1: Wi-Fi

802.11 a/b/g/n

Interface en4: Bluetooth PAN

Interface bridge0: Thunderbolt Bridge

iCloud Quota: 3.10 GB available

System Software:

macOS High Sierra 10.13.3 (17D102)

Time since boot: About 4 days

System Load: 1.43 (1 min ago) 1.54 (5 min ago) 1.52 (15 min ago)

Configuration Files:

/etc/hosts - Count: 10

Security:

Unsigned Files:

Launchd: /Library/LaunchDaemons/com.bombich.ccc.plist

Executable: /Library/PrivilegedHelperTools/com.bombich.ccc

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchDaemons/com.microsoft.office.licensing.helper.plist

Executable: /Library/PrivilegedHelperTools/com.microsoft.office.licensing.helper

Details: Exact match found in the whitelist - probably OK

Launchd: /Library/LaunchDaemons/com.bombich.ccc.scheduledtask.2A90818F-2721-49B5-8AB0-750 72E2E638A.plist

Executable: /Applications/Carbon Copy Cloner.app/Contents/MacOS/ccc_helper.app/Contents/MacOS/ccc_helper 2A90818F-2721-49B5-8AB0-75072E2E638A

Launchd: /Library/LaunchDaemons/com.bombich.ccc.scheduledtask.3E21CA9A-2E72-47D8-929D-31A E341AFE95.plist

Executable: /Applications/Carbon Copy Cloner.app/Contents/MacOS/ccc_helper.app/Contents/MacOS/ccc_helper 3E21CA9A-2E72-47D8-929D-31AE341AFE95

Launchd: /Library/LaunchDaemons/com.adobe.SwitchBoard.plist

Executable: /Library/Application Support/Adobe/SwitchBoard/SwitchBoard.app/Contents/MacOS/launch.switchboard

Details: Exact match found in the whitelist - probably OK

System Launch Agents:

System Launch Daemons:

Launch Agents:

Launch Daemons:

User Launch Agents:

User Login Items:

ConvertoHelper SMLoginItem (Mac App Store - installed 2016-02-17)

(/Applications/Converto.app/Contents/Library/LoginItems/ConvertoHelper.app)

GuidanceLauncher SMLoginItem (Mac App Store - installed 2016-11-22)

(/Applications/Guidance.app/Contents/Library/LoginItems/GuidanceLauncher.app)

goproapp.devicedetection SMLoginItem (installed 2018-01-09)

(/Applications/GoPro Quik.app/Contents/Library/LoginItems/goproapp.devicedetection.app)

com.adobe.SwitchBoard.monitor.plist MachInit

(/etc/mach_init_per_user.d/com.adobe.SwitchBoard.monitor.plist)

Internet Plug-ins:

AdobeExManDetect: AdobeExManDetect 1.1.0.0 (installed 2016-08-11)

FlashPlayer-10.6: 28.0.0.161 (installed 2018-02-06)

QuickTime Plugin: 7.7.3 (installed 2018-01-25)

Flash Player: 28.0.0.161 (installed 2018-02-06)

AdobeAAMDetect: AdobeAAMDetect 1.0.0.0 (installed 2016-08-11)

Flip4Mac WMV Plugin: 3.2.0.16 (installed 2014-06-04)

SharePointBrowserPlugin: 14.7.3 (installed 2017-04-12)

Silverlight: 5.1.30514.0 (installed 2014-10-18)

User Internet Plug-ins:

CitrixOnlineWebDeploymentPlugin: 1.0.105 (installed 2013-04-26)

Audio Plug-ins:

DVCPROHDAudio: 1.3.2 (installed 2014-06-07)

Safari Extensions:

3rd Party Preference Panes:

Flash Player (installed 2018-02-01)

Flip4Mac WMV (installed 2013-03-29)

PreferencesPane (installed 2011-04-26)

Printopia (installed 2014-11-11)

Time Machine:

Skip System Files: No

Mobile backups: No

Auto backup: Yes

Volumes being backed up:

i******k: Disk size: 999.35 GB - Disk used: 450.60 GB

Destinations:

i*************p [Local] (Last used)

Total size: 999.37 GB

Total number of backups: 26

Oldest backup: 2018-02-28 01:35:02

Last backup: 2018-03-03 10:41:46

Top Processes by CPU:

Top Processes by Memory:

Top Processes by Network Use:

Top Processes by Energy Use:

Virtual Memory Information:

Software Installs (past 30 days):

Clean up:

/Library/LaunchDaemons/com.m-audio.firewire.helper.plist

/Library/StartupItems/M-Audio FireWire Audio Helper/M-Audio FireWire Device Helper

Executable not found

Diagnostics Information (past 7 days):

2018-03-03 10:44:17 qmasterd Crash

2018-03-01 13:43:13 com.apple.WebKit.WebContent CPU

2018-03-01 02:31:32 HandBrake.app CPU

2018-03-01 01:48:42 CalendarAgent Crash

2018-02-28 23:40:50 Spin Doctor.app Crash

2018-02-28 19:33:14 Splashtop Streamer.app CPU

2018-02-27 11:21:50 iMovie.app CPU

End of report