I just had my 7.5" barreled .44 Colt at the range this weekend. Using a CED chrono, I clocked several 6-shot strings.
Using .454 round ball and 30 gr Goex, I started out (clean gun) getting high 700s to low 800s feet per second at 7 feet from the muzzle. As the gun fouled up, the velocity increased, and then averaged 841 Fps.
If a Walker can in fact take 60 grains of BP as some here are saying, that would be quite interesting...
The reliability of these weapons, in my admittedly limited experience, is less than I would tolerate in a defensive gun. Saturday I fired about 60 rounds, and had at least 10 misfires (hammer drops and, nothing - upon a secon hammer drop on the same cap, Bang! but you have to fuss around to know if you're dropping on a loaded or unloaded chamber since you have a mixture of them after a couple misfires. Other misfires occured due to a spent cap getting between the hammer and the frame, preventing the hammer from hitting the next cap). Plus, after I was done I noticed that the cylinder lock screw was missing. Ah! That explained why the hammer wouldn't always come back!
I'll take a so-so automatic or a modern revolver over what I'm getting from my Pietta C&B. I'd have to try another C&B or learn how to make it/them more reliable to even consider one as a serious defense tool, when so many guns are available that are better at simply going Bang. And this does not address long-term storage of a loaded C&B gun in potentially humid conditions. You'll have to unload and load more often, which means more cleaning...