I've tested this on an eight-core Xeon X5472 at 3Ghz, with an NVidia GTX 285 and Vista. If it matters, this is a Mac running under Boot Camp. I'll try it on the OSX side some time to compare.
DF is set to 200x100 tiles. Haven't touched anything else except to set sound and intro movies off. I've embarked on a 6x6 area encompasing a human town just to get some movement and activity happening. Tests are from a new save, just letting the game run for a minute without giving any orders.
I'm assuming the second number in brackets after the FPS is the GFPS. It's left at the default 20.
Standard/No: 95-115 FPS. 20 GFPS.
Standard/Yes: Screen doesn't appear to be updating. I can get the menu to appear after clicking a few times, but nothing is rendering at all.
2D/No: 13 FPS & GFPS.
2D/Yes: 13-14 FPS & GFPS.
2DASYNC/No: 13 FPS & GFPS.
2DASYNC/Yes: 14 FPS & GFPS.
2DHW/No: 13 FPS & GFPS.
2DHW/Yes: 13 FPS & GFPS.
So, pretty consistently atrocious on all the 2D modes for me. Any way I can get you more data on what might be happening with those?
PARTIAL:0/No: 105-115FPS. 20 GFPS. No flickering at all, so I won't test with higher partial:N numbers.
PARTIAL:0/Yes: Same lack of rendering problem as with STANDARD. This happened with all the 3D SINGLE_BUFFER: YES options so I've omitted them after this.
ACCUM_BUFFER/No: 105-117FPS. 20 GFPS.
FRAME_BUFFER/No: 105-110FPS. 20 GFPS.
VBO/No: Crash on startup.
So, for me, all the 3D modes bar VBO seem to give basically the same consistent results as STANDARD. No flickering, no noticable artefacts. All very playable. Paused framerates in all the working 3D modes shot up to 1000, the cap, so I didn't include that. I did notice that when I moved the viewpoint deep underground to where there were no revealed tiles the framerate climbed up to ~145 or so, which seems (to me) to indicate that there's still some slowdown coming from the rendering - remove the creatures and structures to render and the simulation speed goes up, despite the simulation itself being unchanged.
Hope my data is helpful. I was wondering, though, could we see an updated and complete description of what each of the 2D and 3D modes does? In the OP of this thread or in the init file itself? I've sort of cobbled together an understanding of most modes from reading the progress of this project, it's something I'd like to see all in one place.