thie highest pound pull crossbow I have herd of manufactured is the Middelton Crossbow at 245 lb draw weight, and is supposed to shoot 375fps orignally it was stated it would shoot 400 fps, last I herd they were supposed to be on the market in July, if you look at them they resemble an Excalibur a lot a whole lot..
heres a link to their site if anyone cares to have a look,,

http://www.middletoncrossbow.com/01.html