Just the thought of a .357 J makes my carpal tunnel and tendonitis flare up.
I read some interesting discussions regarding Colt 1917s converted to .357. Apparently Numrich used to sell a conversion kit with new barrel and cylinder when 1917s were cheap and plentiful. Some who'd never owned one said the frame wouldn't take it because they weren't designed or heat treated for .357, others said the frame is beefy enough that .357s aren't going to hurt it (including one of the principles of the
Colt Fever website) and finally actual owners of said Colts reported they'd never had a problem with frame stretch or timing issues. I fall into the camp of the frame size makes it an acceptable conversion. To me it's not much different than taking a 38/44 and rechambering for .357. As with any sane conversion project, the condition of the base gun and the skill level of the one doing the conversion are where problems arise.
Balance is the reason I settled on ~4" as my Goldilocks size.* The kind of shooting I do doesn't benefit from a longer sight radius or another 50-75fps.
*The only real exception I've found is with the Ruger MK series. I recently shot a 4" and 6" Standard upper (pencil barrel) back to back on the same Standard frame and much to my surprise the 6" balanced better and was more enjoyable to shoot. I really expected to like the 4" more but that just wasn't the case.