A little background.
I've been having problems with games using DirectX graphics for some time, don't quite know when it started however. Frame rates are good on average, but some D3D games have been having a periodic stuttering as their problem. That was not affected by antialiasing or anisothrophic filtering settings - hell, it wasn't even affected by setting all detail to minimum on game settings.

OpenGL games, however, have worked normally. Considering the GPU is a 7600GT with factory overclocks to 650/1600 MHz core/memory, those games should run pretty well so it's not actual performance issue although it feels much like it.
It was quite like having insufficient RAM (or GRAM, or memory bandwidth) for some reason, but some tweaking in RivaTuner seemed to help - specifically, Direct3D blitting settings reduced the stuttering in, say, Lock-On: Modern Air Combat, but didn't quite manage to remove it entirely. In fact, the exact same stuttering phenomenon was there in the dxdiag's Direct 3D tests as well. on a period of about 4-5 seconds, the picture would stutter with low frame rate for perhaps ½-1 second, while otherwise running at perfectly acceptable frame rates. It may not sound like a serious issue, and true enough - it didn't actually make games unplayable, but it was damn annoying nevertheless.

Well, since the school's out and soforth I decided to dig in to the problem. Long story short, I suspected a faulty DirectX installation and consequently ended up re-installing XP (again) to install the latest (April 2007) version of DirectX 9.0c. Well it didn't work but obviously took quite some time. I tried pretty much every ForceWare driver that would work with 7600GT, no joy. Out of spite I finally decided to try out the NVidia's Quadro 160.02 driver instead of the ForceWare series they so fondly like to offer on their driver download pages. The reason was simply that I run out of options - every driver on ForceWare series seemd to be plagued by the same problem. By the way, have you noticed that the latest ForceWare driver (94.24) defaults to the proper (old and good) NVidia control panel?

Seems like they have received some... feedback... on the new fancy interface.
Anyway, on the subject... It appears that the Quadro driver not only works, it also fixes the D3D problems and even offers seemingly better frame rate at least on D3D apps, but it might just feel like that, I haven't done any actual benchmarks on the subject. Often, however, the best benchmark
is how the games feel.
So why am I posting this here? Because I'm likely not the only one who suffers from lower than expected D3D performance. And trying Quadro drivers is quite not the most obvious solution because the ForceWare drivers are the recommendation and should be used if possible, since they likely do have game-specific optimizations and might make some specific games run poorly or not at all.
But if you do have mysterious stuttering with some D3D games, it might be worth it to give the Quadro driver at least a try... I would very much like to know if the effect, or the problem itself, is more widespread or if my PC (or GPU) is an unique case.