Optimise doesn't purely relate to performance - I actually think they quote was that this would have some "GeForce FX specific features", which tends to imply that some extended shader functionality will be used, which would inevitably result in lower performance. I presume that this would be the case with these benchmarks, although given I didn't see any talk about IQ differences (I only skimmed) I would image the effects would be minor.
Looking at the non AA/AF benchmarks though the geometry limitation also stuck out to me - the fact that the 9600XT was consistently behind the 5700 but the 5700 stuck with the 5900 highlighted this quite well. Interesting.