Gamespot have returned to benchmarking Vista now that the service pack has been released. The conclusion states:

Windows Vista with Service Pack 1 is a step in the right direction. Gaming performance increased in comparison to a fresh installation of Windows Vista. Windows XP SP2 provides better overall performance, and remains the place to go for dual-GPU solutions. Windows Vista is not quite the ideal gaming platform yet, but the new OS is getting close to dethroning Windows XP.

To read the full article go here:
Windows Vista SP1 Gaming Performance Report - Features at GameSpot

On a more personal note I've found that Nvidias latest betas (174.74) are very fast and have got to be the best drivers I've used to date.

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AMD X2 6400+ 3.2GHz BLACK EDITION::SCYTHE SAMURAI COOLER::GA-M51 M/B::3GB DDR2 6400RAM::GEFORCE 8800GTS320/625/900MHz DRIVER '174.74' BETA::160 RAID 0 SATA2::SOUND BLASTER AUDIGY/'DANIELS' DRIVERS::LITE-ON DVD RW/PIONEER DVD::HIPER 530W MODULAR::THERMALTAKE ARMOUR Jr CASE::RAZER COPPERHEAD MOUSE::VISTA HOME PREMIUM SP1