How much speed would I gain from going from 100 gr tip to a 90 grain tip, in other words, My arrow weighs 372 gr now if I went to a 90 gr, tip it would around 362, wouls I gain 3 fps, 5 fps, or more??

Well lets put it this way
About the same amount ofsatisfaction a my wife would get if I had ten more millimeters

IMO not that much, FOC would change, that also effects penetration

yeh, I didn't think so, I will stay with the 100 gr tip, bow is shooting 285-289 fps right now, I think that will be fast enough!!!

VA the bow I shot in 2005-2007 shoots 241 FPS, I would say you are fine.

oh yeh, I think so too.. this bow was shooting 309 fps until I realized the pro shop set me up with a 309 gr arrow at 73#!!!!!!!!!!!!

If you look at what % 10 gr is 3.72 so at 300 fps a giant leap of 4 feet per second. Barometric pressure will make a bigger difference.

A couple c hairs.
Opps!