Not sure if I'll help or not but I'm in a similar situation. I shoot the Mathews Outback at 64# with 28inch arrows (which is my draw length) using a release and shooting 100 grain tips. I bought the Axis Obsessions and the Easton chart called for the 400. but it was right there, if I cranked it up at all or if the arrows would have been 29in. it would have been the 340's.. I went with the 400's and so far so good.