First off, let me say upfront that I'm no expert, and what works (or doesn't) for me, will probably be different for someone else.
I have two S&W 329 PDs -- the Titanium/Scandium .44 Mag that weighs 26 Oz. Alternating between the two, I've shot around 2,500 rounds of Magnum Level loads thru these gun since the first of the year. I've shot up to 50 rounds at one time (mostly limit it to 24 rnds plus or minus 5 or 6 time a week) before real fatigue set in. Mine have the Hoque S&W 500 grips on them -- both the wood, and open backstrap Hoques that came with the gun are unshootable for me.
I also have a 340PD (shrouded hammer) and a 360 (exposed hammer) 357 Mags that go 12 oz. I actually split the web of my hand, (requiring stitches) with the factory Hogue Bantam grips and Fed 130gr Factory .357 Mag Personal Defense loads. I would have called someone a liar before experiencing it first hand. I changed the grips out -- the 340 got Crimson Trace laser grips, the rubber ones with the covered back strap. The 360 is wearing Pachmayr Gripper Decellerator's. I have shot .357 loads with bullets up to 185gr (chronoed at 1,000 fps) with these guns and the "replacement" grips. I can't comfortably shoot a full cylinder of full house .357s with either of these guns, and the dread factor is red lining on the second cylinder. With that said, they are fun to shoot with standard 38 special loads.
If you really intend to shoot 200/300 full house 357 Mags each month from one these airweights, you owe it to yourself to try one first. Some people claim they can do it -- I can't and won't -- they just plain hurt with magnum loads.
Several years ago, some guy on the S&W forum reported he had in excess of 5,000 rounds of 357 Mag ammo thru one of these guns and had no problems. If you shoot any gun enough, you will probably experience some problems -- kind of like your vehicle.
Sorry about the round about way of trying to answer your question.
Paul