Hi Champs. I think it totally depends on the bike. Increasing the roller weight means the engine has to work with a lower number of revs, so it has to have more low-rate power. Decreasing the roller weight means the engine has to work at a higher number of revs so you need an engine with less power couple and more acceleration (high-rate power).
Springs are also in the equation because they give the right amount of load to the transmission belt (if it is a belt-drive of course). The belt could slip if you get the springs wrong.
Hope this helps you squeeze some more out!