Yeah I think the 4.5 is quite a bit faster then the 6.5.Mine runs about 47 geared 14/68.No doubt if you want to go over 50 then 5s on the Medusa would be better,or perhaps a working MMM would make the difference,but I really don't want to go there. The 5.5 pro system with 5mm shaft imo looks pretty darn good.It should have close to the output of the older 4.5 but run cooler with lower kv.