Originally Posted by tabetha

It's all about ratios, if you pump less fluid over the same distance the force will be less than a larger cylinder on the same clutch, so for less effort needed the smaller cylinder is what you need.
So a 0.625 will make your pedal lightest, but will it move enough fluid to work it fully ?
If it's on the same car/clutch that you mention having a hard clutch/high bite point, then using a smaller cylinder will make it lighter and move the bite point nearer the floor.
tabetha