25 grns in broadead weight is not going to gain you much speed so I wouldn' t switch just becuase of that. On the other hand, if the 75 grn heads tune and shoot better than the 100 grn heads, I would use them. 3/16" is just enough that it may make a differnce on a very close to marginal hit, but not enough to worry about in my opinion. Shoot the head that gives you the best accuracy and arrow flight.