Mine is 4.9 due to the processor and memory. My video card is an ATI X1950 Pro PCI-E and it rates around 5.9 for Aero, 5.8 for 3d if I remember correctly off of the top of my head.
Here is my machine:
ASUS A8N-E Motherboard w/integrated sound and network card
2 gigs Valueram PC3200 (400 mhz, CAS 3)
300G Raptor SATA 3gbs
ATI X1950 Pro w/256mb, 16x PCI-E
AMD64 X2 4200+
Vista Home Premium
Oh, and it's NOT overclocked in anyway (video or motherboard).
All I know is, Gothic 3 and Oblivion run great. Also, 3dmark05 benched better under Vista than XP for me (by only a couple of hundred points).