iMac slow to respond

SYSTEM SETUP: CS6 in El Capitain. 4Ghz iMac I7 64gb RAM, 2 TB sad drive 500GB available. External 16TB Hardware RAID 0 (3TB available). Photoshop user for 20 years. I had current setup for 1 year with no issues until now.

3 days ago my iMac started getting painfully slow for no apparent reason. I can't remember changing anything. Adobe Bridge has spinning ball before it reacts to any move. In Safari: entering a search term doesn't yield result until I've hit return multiple times. Key commands in photoshop don't immediately work. There's a lag time of 30 seconds before it registers the command. Every time I try to open a photoshop file, the rainbow spinning ball starts. and it takes about 2 minutes before photoshop even start opening the file.

• I tried resetting bridge and photoshop (restart with option+shift+command)

• I deinstalled all adobe applications and reinstalled them.

• used diskwarrior to rebuild directory, and repair permissions on all drives.

• Blackmagic disk speed tests gives me approx 300mb write speed and 2000mb/s read speed on the external RAID, but strangely it takes about 15sec for the program to begin testing and another 15 between read and write tests.

• I've run antivirus and "Malwarebytes"

• disconnecting External drives -> still slow

• switching keyboard

Any idea what might be going on here? what else to try?