I have 4.5 in heel and tip on my 8dn-10's, had 3.6 in the tip with stock exhaust. Mine has the stock mtx spring which is G-Y-G. Only thing I'm worried about is if I go the Hindle route this summer is that I may not be able to get enough weight to keep the RPM's down. Right now I spin 11,400 on firm snow and 11,100 in powder. My YVX has a 41* helix with a green spring @ 3-3 (60*) and I'm also running 19/41 8tooth for my drive but plan on dropping back to an 18 tooth as it take a LONG straight to pull the clucthes 100% with the 19 tooth. I run out of clutch @ 86mph indicated.