To some extent, Magnum Wheel Man is correct - it'll depend on the caliber. I have a Bond Arms Texas Defender model (3" barrel) which sometimes serves "car gun" duty. Currently I have the .38/.357 barrels on it, and CorBon 125gr DPX loads, which
we tested at 1313fps in that gun.
For just shooting at the range, it's fun with light .38sp reloads.
That same gun with the 3.5" .45Colt barrels is a lot less fun to just shoot, and
the power of the various SD loads isn't nearly as impressive. Worse, the thing isn't accurate at all, since only the last half inch of barrel is rifled to accommodate .410 shells.
There are several other calibers/cartridges we tested out of a derringer on our site, if you want to see the results.