More hardware problems, yay!

I've got this system for XP, with an Athlon 64 3700+ (socket 754, nforce4), paired with a mostly idle 8800GT and 2GB of DDR400 along with an Audigy 2 ZS for good measure. And the OS is installed on an SSD because why not.

But when I'm benchmarking it, it doesn't give the same results as I see on the web? For example, on Lost Coast, I get 57.15fps with the benchmark tool, when other people get double that on the internet with the same CPU? In this thread http://forums.gamegrin.com/showthread.php?t=22737 A user gets 100fps. I'm getting the same result whatever video setting I'm using, the 8800GT taking everything with a smile.
I'm getting about 60fps when standing idle at the end of the Half Life 2 introduction, in the train. Everything drops when I get to more crowded areas.
Using FEAR, in the same conditions as this test, I get 56fps on average at 1024x768, while they get 92 (though on a 4000+) http://www.tomshardware.com/reviews/athlon-ga … ark,2054-5.html . My GPU is at about 50% load in that test, but the FPS don't go above 60 when I lower the graphical settings.
With the Dungeon Siege benchmark, I get 75fps average, while they get 132??? https://www.extremetech.com/computing/56478-a … 64-3700/4?print

Additionally, when the CPU is at 100% I can't get smooth scrolling, I keep getting stutters every second or so. Given the CPU is alsways at 100% in all games, I never have smooth scrolling 🙁