Tim Baker found that "On bows of average length and strength, 65 grains (about 1/7 ounce) of weight at each tip affects arrow speed by about 1 fps." [TBB V.1 p. 66].
I just weighed a 1/4" wide x 3/8" thick 4" long "bow tip" of average density osage at 110 grains.
If my math is correct, a 3/8" wide tip will be 30% more massive. In other words, it will weigh 165 grains, so 55 grains more.
So, best case scenario, a 3/8" x 3/8" x 4" tip that is narrowed to 1/4" wide will gain approximately .9 fps.