in reply to my own thread...
iMac 27 , Late 2009
ATi Radeon 4850 512MB
OS X Lion 10.7.3
Kingston 4gb PC3- 10600 204-pin SODIMM
not sure if it still runs at 1066, but with 8gb more, the computer runs smoother & cooler.. i suppose..
got the 16gb for under 100 bucks.. well worth it IMO!!