I can only comment on feel (butt dyno as some eloquently put it) as I dont have the actual dyno graphs to hand, but going from stock to stage 1 made it feel a lot quicker, whilst going from stage 1 to stage 2 made it feel torquier. . . .is that even a word!?!
The pull from 3rd and 4th gear in stage 2 is lovely, probably one of my favourite bits of the car.
With Revo the upgrade from stage 1 to 2 is only £50 I think, the only extra consideration is the cost of the hardware. Try Stage 1 and see if it's enough, if your still yearning for more (it's a slippery slope in my experience) then you haven't spent unnecessarily anyways!
Hope this helps

Tim