GT's are what I'm familiar with, and you're right on the cusp between 3555 and 5575. For the lightest weight arrow for 3D shooting, you could probably shoot 3555's with 100 grain tips. For a hunting arrow, you would need 5575's with heavier tips, anything from 150 grains on up, depending on how they tune. If you wanted a really heavy arrow, you could get 5575's with nock adapters that accept tail weights, and by combining a heavy broadhead with appropriate supplemental weights attached to the front and back inserts, you could have an arrow about as heavy as you wanted.