If I change to weight of my overall arrow weight from 370grn. to 340grn. all else the same will my POI change? How about if I go to 320grn.

It all depends on your bow speed but it should be very minimal for hunting situations.

Edited to say that I thought the grain difference was much smaller. I don't know about dropping that much. But it still depends on your speed and the distance.

My Draw weight is 62lbs. The only thing changing is the overall arrow weight. from 370 to 340 ormaybe 320

dont know how technically accurate it is, but i saw on here somewhere that 5 grains = 1 fps

370 to 320 = about 10 fps

You will most likely lose some KE as well.

IMHO I would be sticking to the heavier arrow.

I am shooting 60lb 28" draw and using 400gr arrows.
They seem to give me the best speed,KE and momentium for my set up.

Exactly my thoughts!