My iMac 2007 27" came upgraded with a Samsung 850 EVO 250 GB SSD. Therefore I think it is irrelevant to look for SATA-2 drives, seems to work just fine with SATA-3 drives.
It also haves the ATI Radeon HD2600 with 256 MB.
Two problems with these machines:
You can not put more than 4 GB of RAM into them. (Yes, 6 is possible, but where you find 4 GB modules?) Why did Apple not put 4 slots into them?
The screen develops yellowish horizontal stripes. Cause is that the LEDs burn the plastic above them.
I would like to know which is the highest specified CPU that was proven to work in these machines.