On my XP SP3 32bit machine with a core2 e8400@4.2GHz, using a GTS250 and 266.58 drivers, I don't get any slowdown anywhere, even in front of confluxes with 2048x1536 background -- but only with shadows off. With them on, I drop down to 24fps in port Jeuno due to a CPU bottleneck. Same thing with an X1950XT and 7.11 drivers at 1024x768 background.