Big Rig,
I also will encourage you to start handloading. To answer your question of velocity loss, it should not go down dramatically. That said, there are many factors involved with revolver velocity that have nothing to do with barrel length. I have a Ruger Bisley 7.5" and Blackhawk Hunter 7.5", both in .41 Mag, and the Bisley regularly shoots 75fps faster than it's stainless counterpart with the same barrel length. From my experience, you can expect to lose about 75-150fps in the scenario you outline, but you never know until you shoot them over a chronograph. I'd count on a 100fps loss.
As for suitable loads, I'd recommend the Cor-Bon 200gr Hard Cast Flat Point loading. That load is about as good as you're going to find for penetration in the .357, which is primarily what it is lacking compared to the bigger rounds. I'd take the non-expanding penetration in the .357, against bigger game, than the lesser penetration of an expanding design bullet anyday. As a rule of thumb, when you want to kill something that seems to big for the round you're using, go with the penetration.