Apple iMac GPU : disinformation at best
Apple use misleading name for their iMac GPU, such as talking about Radeon 2600 Pro for underclocked Radeon 2600 XT, leading to some judgement errors, often trying to hide slower and cheaper GPU than actually integrated 
The old generation iMac has a “Geforce 8800 GS” option, a 8800 GS has 96 processors at 550/1375Mhz, and 384MB ram at 800Mhz with a 192bits interface (nvidia spec for the Geforce 8800GS), and in fact it is a “GeForce 8800M GTS”, that sport 64processors at 500/1250Mhz, up to 512MB RAM at 800Mhz with 256bits interface (nVidia’s official specs). Something that is 30% to 40% slower!!!
The new iMac has officially a “GT130″, with 48 processor cores at 500/1250Mhz, and up to 768MB RAM at 500Mhz with 192bits interface. (Official nVidia Specs here). Notice that memory bandwith is in the level of a GeForce 8600 GT!
In fact the new iMac end-up with a “GeForce 9800M GS”, with 64 processor cores, 256bits memory interface and is given twice the memory speed of the GT130, so it’s probably around 800Mhz. (nVidia official page) Good news finally!
So, the new iMac may be not so bad with it’s 9800M GS, that is equivalent to a desktop Geforce 9600, and probably on the same range of performance as the old iMac.
