I have a customer with an '84 Chevrolet C20, 350, granny 4 speed truck. It leaks oil and he never checks it. The last time I changed it, he brought it in with the lifters clattering. It may have had a quart and a half in it.
I have him on 20W-50 at the moment, and next go around I'll either do the same or 40wt. He also has an '06 Chrysler Town and Country with a 3.8 that burns and leaks oil. It will probably get 30wt next go around.
He's a very busy man with rental properties all over the county, and in spite of his poor maintenance habits, his vehicles just keep chugging along.
I have run a fill of QS 20W-50 in the Roadmaster, and it did great, but my oil pressure has been more consistent on 30wt Delo, and now old 30wt GT-1.
I ran QS 20W-50 in my mom's Craftsman lawn mower with a 21hp Briggs and Stratton for a mowing season, and it looked as good coming out as it did going in. I was rather ashamed to drain it honestly.
I've settled on 30wt being my go to grade for old vehicles/OPE, with 20W-50 a close second. I use 5W-30 and 0W-20 synthetic or blend in the new things.