I have a mid-2010 iMac with a 3.06 GHz Intel Core i3 processor and 4GB 1333MHz DDR3 SDRAM and ATI Radeon HD 4670 256MB GDDR3 SDRAM in my research lab. The person who is using this computer tells me that the computer has gotten very sluggish. At some point the OS was upgraded (from 10.8?) to 10.9.5. There could of course be a lot of reasons for the computer to be running slowly. I am thinking about re-formatting the computer to see if it runs faster. If so, would you recommend keeping 10.9, upgrading to something newer (don't know if that would be even be possible on this older computer), or going back to 10.8? Thanks!