Am running XP catsoup... I couldn't say if games would run slower or not on it, I don't really have anything to compare it to...
I'm not a tweekgeek either so I havn't spend weeks trying to squeeze every last bit from my system either...
The main thing I did was spend a few days before buying it on checking through websites, magazines and forums for what people considered good stable compatible hardware which is nicely clockable (and upgradable cheaply)...
Not that I have clocked it, my theory was that if it was stable clocked, then in default configuration it should be rock solid.. (a theory thats almost worked)
So I ended up with an Abit IS7 mobo 800MHz FSB with 1 gig dual channel ram, celly 2.3c and the ATI raedon 9600 pro..
The other good thing about this mobo was that there were some reports that the onboard 10/100 lan was sometimes a gigabit port, which I can happily confirm..
This is running quite happily at 1280x1024 on most modern games without lag, though there is the odd hog that needs to be switched down if I want all the bells and whistles..
The mobo can take a proper P4, but so far I havn't been able to justify the expense or had the need to...
Back to topic, I think Nairgorn is right in that swapping out models given the scale of things would not give a good enough return for the effort required...