Go with the 340. I did some bare shaft tuning with these arrows last fall. With a 61 lb. Hoyt bow, a 29" 400 series Axis ST (100 gr. field point) was perfect. Going up to 70 lbs, you would surely want a 340, unless you were planning to cut your shafts to 27". At 27" or shorter, with a 100 grain head, the 400 series would be good for 70 lbs.