IF your form is absolutely perfect in the worst field conditions, IF your bow is perfectly tuned, IF you have absolutely perfectly tuned arrows and IF nothing goes the slightest bit wrong, then 3" vanes might stabilize Montecs okay. If you can' t guarantee all those things, then you' d better go to 4" .

If you want less weight than 4" vanes then switch to 4" feathers. They' ll be about the same weigh as 3" vanes and give you more stabilization than 4" vanes will.