Mavericks isn't the issue. It's what users have installed on their systems that is causing issues with Mavericks operation.
How much RAM installed on your Mac?
How full is your Mac's hard drive?
Do you have any antivirus installed? Antivirus software can negatively impede the normal operation of OS X.
Do you have apps like MacKeeper or any other so called "cleaning" maintenance apps like CleanMyMac 1 or 2, TuneUpMyMac or anything like these apps, installed on your Mac? These types of apps, while they appear to be helpful, can do too good a job of data "cleanup" causing the potential to do serious data corruption or data deletion and render a perfectly running OS completely dead and useless leaving you with a frozen, non-functional Mac.
You may have other incompatible or software that hasn't been updated to compatible Mavericks versions.
If you wish, Please download, install and run Etrecheck.
Etrecheck was developed as a simple Mac diagnostic reporting tool by a regular Apple Support forum user and technical support contributor named Etresoft.
Etrecheck is a small, unobstrusive app that compiles a static snapshot of your entire Mac hardware system and installed software.
This is a free app that has been honestly created to provided help in diagnosing issues with Macs running the new OS X 10.9 Mavericks.
It is not malware and can be safely downloaded and installed onto your Mac.
Copy/paste and post its report here in another reply thread so that we have a complete profile of your Mac's hardware and installed software so we can all help with your Mac performance issues.
20 GByte Ram should be enough
About 883 Gbyte free on my 1 TByte system drive (other drives have a higher % free). I've considered a possible disk fragmentation. On my last Apple system, I did an OpSys upgrade which massively fragmented my disk, slowing system performance. Defrag helped. I know of no degrag SW available and it apparently no longer needed. In 15+ years of UNIX system experience, I never once had to defrag a disk, it just was never required.
No antivirus SW. I'm thinking it may be beneficial, BUT as you imply, it is good to be able to turn it off since it could impede system performance.
I have no "cleaning"/maintenance SW installed on my system--such SW is advertises at various websites, but it all looks suspicious to me.
I updated every (Apple) app that required updating after the Mavericks download, took me almost another full day to dowload and install.
To be clear, my system is not snail-like slow. Just a quite noticeable slowdown in things like app loads to memory.
I will try Etrecheck, see if it helps. And I'll let you know the results.
Mac Pro (Mid 2010)
Mac Pro - model: MacPro5,1
2 2.4 GHz Quad-Core Intel Xeon CPUs: 8 cores
20 GB RAM
ATI Radeon HD 5770 - VRAM: 1024 MB
OS X 10.9.2 (13C1021) - Uptime: 0 days 5:10:42
HL-DT-ST DVD-RW GH61N
WDC WD1001FALS-41Y6A0 disk1 : (1 TB)
EFI (disk1s1) <not mounted>: 209.7 MB
Macintosh HD (disk1s2) / [Startup]: 999.35 GB (883.26 GB free)
Recovery HD (disk1s3) <not mounted>: 650 MB
LaCie Rikiki USB 3.0 1 TB
EFI (disk0s1) <not mounted>: 209.7 MB
LaCie (disk0s2) /Volumes/LaCie: 999.86 GB (402.7 GB free)
Apple, Inc. Keyboard Hub
Macally Peripherals Macally BUMPERMOUSE
Apple Inc. Apple Keyboard
Apple Inc. Display iSight
Apple Inc. Apple LED Cinema Display
Apple Inc. Display Audio
Apple Inc. BRCM2046 Hub
Apple Inc. Bluetooth USB Host Controller
G-TECH OEM ATA Device 00 800mbit - 800mbit max
disk2s1 (disk2s1) <not mounted>: 32 KB
G-Drive Mini (disk2s3) /Volumes/G-Drive Mini: 499.97 GB (492.62 GB free)
Mac App Store and identified developers
[kext loaded] com.ATTO.driver.ATTOExpressPCIUl4 (4.4.2) Support
[kext loaded] com.hzsystems.terminus.driver (4) Support
[not loaded] com.roxio.BluRaySupport (1.1.6) Support
[not loaded] com.roxio.TDIXController (2.0) Support
[loaded] com.adobe.fpsaud.plist Support
[not loaded] com.attotech.attomgtd.plist Support
[running] com.intego.BackupAssistant.daemon.plist Support
[loaded] com.intego.backupassistant.agent.plist Support
User Launch Agents:
[loaded] com.adobe.ARM.[...].plist Support
User Login Items:
Flip4Mac WMV Plugin: Version: 188.8.131.52 - SDK 10.8 Support
FlashPlayer-10.6: Version: 184.108.40.206 - SDK 10.6 Support
Default Browser: Version: 537 - SDK 10.9
AdobePDFViewerNPAPI: Version: 10.1.9 Support
AdobePDFViewer: Version: 10.1.9 Support
Flash Player: Version: 220.127.116.11 - SDK 10.6 Support
QuickTime Plugin: Version: 7.7.3
iPhotoPhotocast: Version: 7.0 - SDK 10.7
AdBlock: Version: 2.6.28
Video Converter: Version: 3.1.0
BluetoothAudioPlugIn: Version: 1.0 - SDK 10.9
AirPlay: Version: 2.0 - SDK 10.9
AppleAVBAudio: Version: 203.2 - SDK 10.9
iSightAudio: Version: 7.7.3 - SDK 10.9
Quartz Composer Visualizer: Version: 1.4 - SDK 10.9
3rd Party Preference Panes:
Flash Player Support
Flip4Mac WMV Support
Time Machine not configured!
Top Processes by CPU:
Top Processes by Memory:
410 MB mds_stores
184 MB Safari
164 MB Shrook
164 MB thunderbird
143 MB com.apple.IconServicesAgent
Virtual Memory Information:
15.25 GB Free RAM
3.04 GB Active RAM
306 MB Inactive RAM
1.40 GB Wired RAM
470 MB Page-ins
0 B Page-outs
Having OS incompatible third party hardware installed and incompatible or non-updated software that runs that incompatible hardware can definitely have an impact on your Mac's and OS performance.
If the added third party hardware is completely incompatible with the Mac and current OS X version, it can cause OS X Kernel panics and freezes.
It could explain your Mac's continued slower performance issues.
Open Console app and look at All Messages. You can scroll through the log list and look at the system log (or any of the others), but All Messages consolidates most of the important ones.
Open Activity Monitor and look at the Memory and CPU tabs to see what is using most of the resources. You can sort the list by memory/CPU%.
It seems Spotlight is working overtime (mds_stores). Has it completed the initial scan? It shouldn't be working that hard unless it is doing the initial scan.
You can reset the spotlight index like this: http://support.apple.com/kb/HT2409
If you are completely unable to load websites, then it would be best to find out what was causing that before upgrading. You could easily re-install the same software on Mavericks and cause problems.
Can you define what you mean by "slow". And can you do with without BitTorrent running?
You seem to have a kernel extension from Toast. Make sure that is up to date.
If you want to look at log files, they are all in /var/log. Most of them are in Console.app too.