Sporadic performance with Fear and FearXp

I've installed the official ATI drivers for my X1900XT and downloaded the
windowsupdates, which had a small patch for my motherboard. I also posted
this message in the FEAR tech forums to see if I'm the only person.

So far and only in Fear do I get benchmarks numbers that jump around a bit,
but namely each consecutive run of the benchmark tends to get me a lower
number.

For example, at one point I was getting 100 fps, then I dropped down to 75.
Then down to 63, then down to 30. Exit out, go back in and I might score a
85, then a 41 than a 20. An interesting side note, is I can go in an turn
off shadows and Volumetric lighting and get the exact same score (which is
normally when it's saying 50 or less)

Other games I've benchmarked are Doom3 (at 1.03) and Half-Life2:Lost Coast
and they give me the same results (+/- 2-3 fps) every time I run them.
3Dmark06 has given me consistent numbers as well.

So I'm not sure if it's a memory (probably video) leak or just the way Vista
handles the game.

Running the benchmarks in XP:SP2 mode and as an Admin didn't make any
difference either.

Other than FEAR, Vista performs acceptable well (though slower) than XP.

Doom3 scores a 119 versus 132.

HL2 scored a 131 versus a 142

3Dmark06 scored a 5976 versus a 6063.

FEAR so far as done the worse, with the best score being a 85 versus 120.

I've tried to be methodically with my testing, but I can't seem to determine
if the problem is on my side (a configuration setting) or it's just the way
it is right now. Any thoughts or suggestion you have I wouldn't mind hearing
them

Thanks

Dale