Update for Cornered Rat:
For a really light load with OTBC 125-gr TCs, try 4.3 of WW231. Out of a six-inch, they go about 750 fps and generate very little recoil. OTBC's book lists 4.2 as the minimum.
Methinks they'd be good for training, too, as they run through speedloaders easier than the traditional 148-gr wadcutters.