I am new here, and probably shouldn't be helping yet, but I have just gone thru this and will add.
I am using carbons,30-50lb spine. I am shooting around 43lb.
I left mine full length, 32inches, and just squared the tips. Then added inserts and fletched. Using 125 grain tips just to see what happens, and they fly perfectly so far. I am going to try 150 grains, and maybe some heavier inserts.
Multiply arrow length X gpi in shaft weight. Then choose the weight inserts and broadhead to match, to get you close to 500 grains weight for arrows.
I would say you are gonna just have to break down and shoot both types, but will bet that the 40-60s will spine better with all the weight you are gonna have to load up front, if that is the route you choose to go.
I started out with the arrows full length, and will add weight until I get close. IF the weight I add is too much and weakens the spine, then I will cut them back an inch at a time, until I can't go back farther. IF they still spine weak, then I will jump up in spine and start over with full length and the highest weight that I attempted with the previous spine.
Just an absolute novice's advice and observation, but- it seems that with the weight you are pulling, that 50 lbs is more within a "workable" weight range on the 40-60s than the 30-50's. with the 30-50's, you are starting at the top of the spine spectrum, so to speak, so you dont have too much room to play with weight(adding weight) before you weaken the spine.
As a novice, I come from (and still shoot) a compound. carbons are great-but I am finding it difficult to load up weight without adding most of it up front. Front side weight doesn't seem to be too detrimental so far, but I am sure there is a threshold there somewhere, where it becomes too much.
Good luck,
Farmer