Heck, even with black powder loads using ffg, you should be able to launch a 255 grain bullet in the 900fps ballpark! That's what they were throwing them in 1873!
In a Colt sized handgun, that is a good velocity and a decent amount of recoil. With the New Vaquero, I have no doubt you could go faster, but I'd simply stop at 900 to 1000 fps and be satisfied.
That will kill a buffalo!
Dan