Firstly, welcome to the board.

I came across a US site some time ago which showed some air rifles that produced in excess of 600 fpe and were .50 calibre.

Dont know how accurate these things were but I'm sure with that power and pellet size/weight a well placed head shot from a sensible range would be capable of dropping both dear and turkey. I'll do a search and see if I can find the web site and post a link.

Happy shooting....Ian