If you don't own arrows, yet. The question I'd ask is. "What are you trying to accomplish?" My answer to that question is: "completely perfect bare shaft flight, then broad head consistency (consistent is very different than accurate). I'd like my set up needs to deliver broad heads, every time, on the spot. No weird "flyers" or inconsistency. i don't care about speed. Ever. "
It is a bit off the beaten path, so here we go.
I target 18+% FOC and I am not a believer in "stiff is always better". I can't make it work. There seems to be a significant and absolutely visible consistency jump around that number. Its like the arrows are magic and stack up tight with very little effort on my part. Are they a bit slower, yes, but man, the consistency is just hard to believe.
Current setup is 67lbs 27.5" draw, 28 1/4" 400 spine arrow shooting a 125 grain point and 100 grain brass insert. They will shoot with no fletching as far as you want to and hit with the nock right behind the arrow. Broad heads, Magnus Stingers (the new Black Hornet is totally nasty too) are preferred, it shoots muzzy's, montec, basically whatever. I do not shoot mechanicals (I did, though, too many "weird" losses and penetration was always suspect).
I realize I am totally cutting against the grain on a message board with this many experienced folks, but my recommendation to you is 340 spine, shaft cut to your preferred length and 225 grains up front. If it doesn't work, that's ok, you jump to 300 spine. You'll find carbon arrows are very, very, forgiving on the "softer" side. If you jump off the bridge and give this a rip, find a traditional guy or someone to help you increase point weight.
As noted above. If you want perfect broad head flight, give this a chance. If you want the fastest set up, that is not my specialty.
Have fun out there with whatever you choose. There's a bunch of ways to skin this cat.