[DESKTOP] Core2Quad Q6600 2.4GHz / 4GB RAM / WinXP
[ONBOARD] Intel(R) G33/G31 Express Chipset Family - 280 FPS
NVIDIA GeForce 6200 LE - 90 FPS
NVIDIA GeForce 8600 GT - 1245 FPS
[DESKTOP] Pentium D Dual Core 3GHz / 3GB RAM / WinXP
NVIDIA GeForce 6200 LE - 60 FPS
NVIDIA GeForce 8600 GT - 1230 FPS
[NOTEBOOK] Core2Duo T8100 2.1GHz / 2GB RAM / WinXP
[ONBOARD] Mobile Intel(R) 965 Express Chipset Family - 280 FPS
NVIDIA GeForce 8400M GS - 330 FPS
With the first test, the 6200 takes 11ms, while the 8600 takes 0.8ms, so the 8600 is about 14 times faster.
With the second test, the 6200 takes 17ms, while the 8600 takes 0.8ms, which is 21 times faster.
So it's not quite as bad as you might expect. Not to mention the fact that SFML 1.x is quite outdated, so being slow is to be expected.