What;s the difference between 3-49's and 3-71's (and for goodness sakes don't say "22"..lol)? Is it weight?

Let's say I was gonna get a few a/c/c's made up to just hunt whitetails with, this fall. 71lbs. draw weight on the Ally.....29" draw....and I think my arrows are 27-1/2". What arrow would I get? I don't mind a heavier arrow AT ALL.....and I'm wondering what would be the DOWN side of choosing the heavier arrow.