So it seems that Minecraft performance does rely heavily on the gpu, whilst before i thought it was mostly cpu based. A couple of days ago I bought KOTOR off Steam and it turned out I was getting a crappy 15-20 fps performance most of the time. My specs aren't great but they should be more than enough to run KOTOR at least (2.66ghz Pentium 4/Geforce 6200).
I presumed it to be a driver based issue at first so I've tried loads off different ones and finally leaving it at a random modded one from a few years ago (older drivers a usually considered better for a gpu of this age anyway). Unfortunately, FRAPS showed no change to KOTOR's framerate so my next step was to overclock the 6200 with Ntune, going from 300-350mhz. This did give me about 2fps more in KOTOR, but really only moves it from 10 steps to 9 steps from being playable (enjoyably at least). Anyway right now for that game I've pretty much given up trying to find the right optimisation and are suffering through with a crappy fps (still a good game though). Although weirdly the game acts like it's cpu limited, since changing resolutions only produces relatively small changes in framerate (it is rated for something like 1ghz P3s).
Anyway, back to Minecraft, I started playing it again today for the first time after GAFocalypse and to my astonishment I can now get 25-30fps average with the minimum fog level! To put that into perspective I was getting less than 5fps with the equivalent settings previously (I spent most of the time with maximum fog and an average fps of something like 30-50).
So I guess the moral of the story is for anybody who has an older and crappier gpu, like me, try testing out a few older and modded drivers, you might be surprised by the difference it can make. Overclocking a bit might help as well.