What you are shooting right now is enough to "wallop" any deer and keep going after a pass through. According to GT's website you are shooting a 5575 that weighs 337.2 grains (close to your 338) and this is enough for deer sized game. With standard nocks and inserts and a 75 gr head the FOC is 9.3%. OK, but not ideal. The usual accepted rule is somewhere between 10% and 15% FOC. I've shot arrows anywhere from 7% to 17% and gotten the job done. Rules are made to be broken and sometimes changed.

FOC is what helps keep the arrow on track at longer distances. The arrow has to have enough point weight to pull the arrow along. Too little and groups open up at longer distances. The 9.3% might be OK for most deer hunting yardages, say 30 yards or less. After that the arrow may tend to wander. 100 gr head might be advisable. Best way to find ut is to get some 100 gr field points and see if the arrows group tighter at 25 yards and longer; especially if you expect to shoot beyond 30 yards. Shoot them at a distance equal to or beyond the longest distance you expect to shoot at deer.

Going with the heavier head you might expect to slightly retune the bow and most likely resight as well. You have all summer. Get to it.