I found out about the buffer yesterday and it helped me a lot on my laptop.
I think it depends which part of your machine is having a hard time with the game.
In my case, my Windows 7 Laptop has an I7 processor, which has it easy. My GPU (Nvidia 360m) on the other hand, has trouble keeping up.
So, I was pushing the game on a 1200x720 resolution, all effects on, normal/high texture settings, but low shadows and no fancy AA/multisampling/whatever or I would get hit by a major increase of lag and frame rate drops. The game was OK when I was alone in an area, but did not respond very well in busy areas, where it could even lag up to the point of crashing. My mouse was also lagging half a second, but I didn't mind that, because I play with a 360 controller hooked up. Anyway, annoyed with the crashes in busy areas I decided to cut the buffer in half. Now, the game response became smooth as silk everywhere and the mouse lag was nearly non existant. I just couldn't stand the look though. Aside from the rich textures and animations, it looked like playing Tomb Raider in DOS. So I played around with the buffer and found 4/3 was perfect for me. I even upped the shadow details a little :)
Now on my old Desktop it is the other way around. It is an older Intel2 Quad PC and it had a 8600 card. We replaced the 8600 with a GTX 460. The GTX 460 clearly has an easy time with the game, so we maxed a bunch of settings, but the quad processor didn't like that. It would constantly stutter no matter where you looked or where you were in the game. Having the Task Manager performance tab open on second screen made it clear the CPU was capping out during stuttering. So we changed buffer size, resolution, texture settings, etc. but that all didn't really help. Changing stuff in Windows (Vista in this case btw) like disabling indexing service and windows update, but also closing some background programs, like audio mixer from our soundcard and virus scanner. Then running the game full screen on a single monitor instead of dual monitor + window mode and voila: game is smooth! High-res, all features enabled. Processor no longer capping out (about 70~80%).
Only turned "Field of depth" off in the config, as that made the trees in game flash and act funny :)
So.. Maybe dropping buffer size really helps those who have bad Graphic Cards, while low CPU users will have to resort to other things.