27" Mid 2011 iMac really dogs using Photoshop CC and Lightroom 5...

Hello, see how many of these you can answer...

See if the Disk is issuing any S.M.A.R.T errors in Disk Utility...

http://support.apple.com/kb/PH7029

Open Activity Monitor in Applications>Utilities, select All Processes & sort on CPU%, any indications there?

How much free RAM & free Disk space do you have also, click on the Memory & Disk Usage Tabs.

Open Console in Utilities & see if there are any clues or repeating messages when this slowdown happens.

In the Memory tab of Activity Monitor, are there a lot of Pageouts?

It depends on how long your CPU has been running since pageouts/swap space reset upon reboot. But, yes, this is alot. Page outs are generally a sign that you need more RAM to run the applications you are running. They occur when you use your HDD as a scratch disk once you run out of physical memory. Your RAM is forced to 'page out' (write) to your HDD in the allocated swap space, which greatly slows down performance of your machine. I would recommend upgrading your RAM for the software you are using as your machine's performance is suffering and this activity is unhealthy for your drive in the long run.

You can have it done at Apple. Installing RAM is actually quite simple, as long as you have a small screwdriver and are careful. It will be much cheaper to install RAM yourself.

iMac: How to remove or install memory - Support - Apple

iMac (Mid 2011): Memory specifications - Support - Apple

Order from crucial, if you do custom. They offer 1 year warranty on all their RAM and are highly reputable. Note crucial specs indicate your model supports 32 GB RAM, rather than Apple's 16 GB. Go by crucial's specs.

http://www.crucial.com/store/listparts.aspx?model=iMac%20%2821.5%20and%2027-inch %2C%20Mid%202011%29&pl=Apple&cat=RAM

I would order either the 8 GB kit (2 x 4 modules, 16 GB RAM total), or the 16 GB kit (8 x2 , 24 GB total).

Your iMac can take up to 32 GBs of RAM.

Correct and reliable Mac RAM can be purchased from online Mac RAM sources Crucial memory or OWC (macsales.com).

If you are not from the U.S., both OWC and Crucial Memory have international shipping. Crucial has various websites that cover the different regions/continents of the world.

I suggest you install, at the very least, another 8 GBs of RAM. Install more If you can afford it!

Between the high processing overhead of OS X 10.8 Mountain Lion and With all of the high computer resource apps you run, the more RAM you can install, the better.

Installing RAM in an iMac is easy.

http://m.youtube.com/watch?v=k8Sj10wYXAI&desktop_uri=%2Fwatch%3Fv%3Dk8Sj10wYXAI

80MB fre is a problem, but I think you have an errant process.

One way to test is to Safe Boot from the HD, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, Test for problem in Safe Mode...

PS. Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive

Reboot, test again.

If it only does it in Regular Boot, then it could be some hardware problem like Video card, (Quartz is turned off in Safe Mode), or Airport, or some USB or Firewire device, or 3rd party add-on, Check System Preferences>Accounts (Users & Groups in later OSX versions)>Login Items window to see if it or something relevant is listed.

Check the System Preferences>Other Row, for 3rd party Pref Panes.

Also look in these if they exist, some are invisible...

/private/var/run/StartupItems

/Library/StartupItems

/System/Library/StartupItems

/System/Library/LaunchDaemons

/Library/LaunchDaemons

Great to hear, thanks for the report! 🙂