I find 60# is the sort of change over point where either is ok. at 70# you really need the 11/32.
For distance the 5/16 is prob' better. but you might need a 150gn point to calm it down a tad. Too light and it can get a bit hand shocky/elbow jarring.
Bottom line is try it and see. Avoid the over large fletchings that some
longbow archers seem to go in for, I reckon 3" is plenty. If it needs bigger fletchings to stabilise the arrow, the something el;se (prob spine ) is wrong.
Remember the shaft accounts for more weight than the point.
Note:- With 30" draw you may want to go up in spine.
Del