You're missing WAY to many vairables for a solid answer. However you yourself provided a good starting point. You said "5 inches at 55 yards" that tells me your range is well inside 55 yards. Why?
- I am assuming that is known distance, warmed up, on a target, with good footing
- None of which applies to hunting where its a possibly known distance (did it move after you ranged it?), you are NOT warmed up, you probably don't have great footing and can't stand rock solid up right.
So I figure an average persons effective range drops by ~30%, so you are down to around 40ish.
Work your archery skills until you can hold less than 1 inch for each 10 yards. Effective kill zone is about 5-6 inches on a whitetail. Shave a bit off that since you really can't see the edge, and you get "how far away can you hit a 4 inch circle pretty much every time".
After that the bow, arrow, broadhead all make a huge difference to penetration. Sure light arrows leave the bow fast, but they slow down faster than a heavy arrow, so at some point the speeds equal, then swap.
Way more to the question that you meant, but it really doesn't take much arrow speed to penetrate into the chest of a deer if you have the right arrow and broadhead.
You say 25 inch draw length, that's pretty low so you are somewhat limited on speed out of the gate, but it can be done.