I know one thing. Growing up in the mountains of Pa and driving up and down them to and from my grandmothers house with my old 68 Impala with a 250 hp 327 with 88k miles on it, if I let it coast down the mountain, (a 4 mile descent) by the time I got to the bottom it was smoking pritty good out the exhaust. But with normal driving it didn't smoke a lick. Just when I was going down and letting the engine keep a slow ride down using the brakes some as well. That engine had nothing but QS in it from the gentleman I bought it from. When I got it I had the engine rebuilt at 100k, ( was going into the Air Force and wanted to make sure it was dependable) After taking the engine apart I was surprised to see how clean it was inside, espesially with everyone hating QS oil. It had it's little build up around the distributer but nothing really major for a 100k engine with 4k oil changes. I put 300hp heads on it, the double hump ones and a blue printed 300hp crane cam and what a difference it made.
But back to the subject at hand. We always used the engine to slow down and never had any problems with anything, drive train nothing and that was in both our standards and AT's. Heck our 72 square back VW made it to 140k before it threw a rod on #2 cylinder and I was told that was a normal thing due to that cylinder not getting cooled like the rest and usually didn't last as long as what we got out of it. Oh and it had the original clutch on it as well.