Yes,
.357 cases will signifigantly reduce pressure/velocity, but the upside is some gain in accuracy by eliminating some bullet jump. I have proved this with a 686, DEWC seated to groove, from a ransom rest.

What we did was find the most accurate load with .38 cases, then duplicate that velocity in .357 cases (working up from our .38 load, and a little beyond to see if group improved, it did not). We were using clays, 2.2gr in 38, 2.7gr in .357, yeilding just above 700fps. This cut about an inch off this particular guns group @25yds.

Personally, if your using .357 cases I would be inclined to use very bulky powder, theres a lot of space to fill with very little powder, my buddy refused to deviate from Clays.