I assume the Nvidia drivers is actually 2 seperate sets of drivers, one for XP and one for Vista. The XP are mature and include a more comprehensive set of profiles, the Vista are new and they probably haven't bothered.
Of course seperate drivers could explain the difference by themselves.
That's why I suggested a gaming intensive benchmark might be more conclusive than the 3dMarks. One you could set an optimum profile for. Or for that matter if there's a "Fraps for Vista" out use that on a recent game you have installed, it's less effort.
Nuts, thinking about it I wonder if Nvidia has even had the time to include SLI game profiles in the Vista compatible driver releases yet? Ah, alpha testing software, I do it about 1 week a month, but at least get paid for it. (The Nvidia drivers are still in alpha, Vista is further along than that now.)