I get 1,600 fps (Chronoed) with 300gr factory and reloads in my 6" FAC .454 Field Grade. 340gr stuff about the same.
To me, the 6" FAC is the best balanced gun I own. It just kind of sits in your hands -- not muzzle light, but not muzzle heavy.
8.0 gr of Titegroup and 200gr SWC (.45 ACP Bullet), crimped over front drive band shoots to same point of impact at 25 yds as the 300gr at 1,600 fps. Should be about 1,100 fps and makes a nice light load.
Forgot to mention -- it sure beats the crap out of the knuckle on my middle finger.