RE: PSE impala
In the latest Traditional Bowhunter Magazine a 12 year old has taken a deer with a 33@22 longbow, and a female archer took a NICE bull elk with her 46# Longbow. With proper arrows, and shaving sharp broadheads I believe45 will get the job done. There is a thread going down at the bottom of the page on this very subject. There is alot of good info in there.
Good luck