If it helps,I shoot Dan Toelke Whips,54# @ my 29" draw with three 5" feathers and 400's & 500's both shoot well when length from back of point to throat of nock is 30 3/8" and the 500's have two 100 gr. brass inserts and 145gr. field pts., filling the last 3" or so of the shaft with inserts & field pt. effectively shortens the shaft and stiffens spine and allows use of the points that easily extract from 3d targets. 400's fly the same with a 50 gr. brass insert and either 250 grain field points or a combination of steel inserts/broadheads at or a bit above 250 grs. Both set-ups provide 22% f.o.c. and weigh 650-660 grs. My experience has been that carbons are MUCH STIFFER than charts indicate and I would suspect you will have to put a lot of weight up front for 340's to fly well out of your set-up.