If you are seeking a vehicle to explore the outer limits of handloading for .357, then surely the Ruger is your better bet. If you want the smoothest shooter, then that would be the Smith.
I have not personally encountered anyone who's has ever shot a K-frame out-of-time. If you mean increased endshake, or flame cutting of the topstrap, then yes. Endshake, or the fore-and-aft movement of the cylinder on the crane, can be corrected by fitting the proper width of shim(s). Flame cutting goes only to a point, them appears to wear no further, which is really a cosmetic issue. In any case, that's why the L-frame was created.
Rapid fire is supposed to be the culprit with timing problems, but I have only seen this evidenced in Colt revolvers. I've handled them NIB that were not right! The mass of the cylinder is set into abrupt rotation by a relatively small, thin hand, or pawl, then promptly halted by a tiny bolt or cylinder stop. But, both of these parts are braced by the edges of the frame windows from which they protrude. It would seem to me that the greater the rotaional mass of the cylinder, the more propensity there would be for this to occur. The L-frames would be more of a concern, whereas the J-frame would be less so.
C.R., I do respect the wisdom of your years, and your experience. However, I do not think that stainless steel is the issue, as the internals of Smiths have always been chrome-moly. Though, at first, they were electroless nickle coated to match. Now, I've read elsewhere that they've gone over to MIM internals, though they are finished in a case-hardened appearance. If THAT is true, then there may be cause for some concern with undue wear. I have limited knowledge of sintered metal production, but I am put-off by it. If I need some correction here, please let me know.