My FSO setup is probably something of an outlier, but this is what I use:
FSO builds: 9/17/05, along with whatever the latest one is
Command lines: -spec -glow -jpgtga -dualscanlines -targetinfo -ballistic_gauge -3dwarp -snd_preload -env -alpha_env -fps -allslev -ambient_factor 90 -ogl_spec 80
VPs: All 3.6.8 media VPs, with zero byte tbm files in \data\tables to override the ones in the VPs
Other settings: 2048x1536, 16x AA for OGL / 8x AA for D3D, 16x HQ AF
These settings give a constant 85fps at all times and play very smoothly on this hardware:
Opteron 146, running at 3003mhz
1024MB value memory, running at 187mhz 2-3-2
7800 GT SLI, both running at 500/575mhz
In your FAQ I think you should mention the ambient factor setting in particular. The default value for this is terrible in my opinion and changing it to 100 or less makes OpenGL mode look far better. Also, -env and -alpha_env only work in 9/17 and crash the game in D3D in most newer builds (OGL ignores these flags), but it works out okay since I don't use D3D except in 9/17.