I fire +p ammo in my K-frames as well as my j-frames. Unless you're very rich, you can't afford to buy enough +p ammo from the major manufacturers to hurt a K-frame. It is pretty much the same with the all-steel j-frames. I have fired a bunch of +p in my Model 36s and Model 60s. The +p ammo from the major manufacturers is really pretty anemic.
The Buffalo Bore +p 158 grain lead swc hollow point is a different story. I shoot it in my j-frames to sight in, and I carry it in my Models 60 and 36 for defense, but it is truly a hot little round. In my mind, it makes a j-frame a very viable personal defense round. The manufacturer reports over 1000fps from the round in a two-inch barrel, and that ain't to be sneezed at. I wouldn't want to spend a day at the range shooting the BB stuff from a j-frame or a K-frame. It is also very expensive.