I have a few 4 stroke 50cc's and I only use 3 of the rollers instead of 6. It gives me noticably more take off and doesnt affect my top speed at all. I dont have sliders yet just the stock variators but with MRP 6 gram rollers. BUT the thing is, after you use 3 rollers for a while, you have to switch them out for the other 3 rollers and put them ones in the other three slots, the ones that you didnt have 3 in previously. Keeps things wearing even. I have always used only 3 rollers with no adverse affects.
I have 4500 miles on a set of three rollers and still running great!
I havent decided what other upgrades im going to do with them scoots yet but just the roller change made a huge diff.* not sure if this will work in 2 Strokes but I dont see why it wouldnt *