Crucial 1TB SSD in old iMac?

I would like to have an iMac with 1TB of SSD, however I can only get three quarters of that with the new ones. But, just recently Crucial announced one at $0.60c/GB and that came to about £400, wow I thought! They say that it is compatible with older iMacs and that is fine by me but I was wondering where the cut off point was, what year/model?

Has anybody ever fitted a 2.5" HDD/SSD in an iMac before, is it simple?

Crucial also say that no Mac is capable of 6Gbps SATA III and so they lowered it to 3Gbps, is it true?

ref:

http://www.macworld.co.uk/mac/news/?newsid=3419897

http://www.crucial.com/uk/store/partspecs.aspx?IMODULE=CT960M500SSD1

Thanks!