While 32-bit client is fairly rigid at observing foreground and background FPS caps, 64 bit seems to have issues on my machine in that regard.

Low slider values (50 FPS or less) seem to be enforced properly.

Medium values (60-70 FPS on 32-bit client) give very erratic FPS jumps in 50-90 FPS range, regardless of whether a large scene is displayed or I'm looking at a wall in first person.

High values (90+ FPS on 32-bit client) seem to cancel the cap outright and the video card skyrockets to 200+ FPS with all the heat that implies.

My system is:

i7 2600 / 8 GB DDR3 / Radeon 6950HD / Windows 7 Ultimate.