Muso,
I shoot carbons from my Berry's and I too shoot 3U.
I nock "around" 1/2", the vixen likes just shy of 3/4 and the others between 1/2" and 5/8".
At 30" I'm gonna guess you might need around 175gr up front depending on the shelf cut.
Personally, to get away from guessing I'd suggest a simplified bare shaft tuning. I follow Byron Fergusons method of tuning, and in the grand scheme of things it may not be the BEST tune you can get but for myself it is. Also it works for Byron so I'm sure it will work just fine for me. I can TRY to explain it in full detail for you but honestly I suggest picking up his DVD "tuning for extreme accuracy" . I did a review on it a while ago and it have done absolute wonders for me and my confidence.
My 2 cents