well, and considering that everybody here is probably running a different weight oil in the same motors, I doubt if the mixed grades makes any difference.
Like Aggie ran just fine on 20-50 during break-in, then I switched to 10-40.... It's all greasy, and mixed bucket-man, he was probably getting a pretty consistent brew....
now as to WHAT you run, I say there is definitely a difference.
You pop the valve cover off an engine that has never been off before, and has been running CHEAP oil and not changing often enough, I know you have, -if you haven't, you should- there's about half an inch of FAECES clotted all over everything.
More expensive oils, less WAXy crap, less fecal contamination.
I personally would not run Walmart Super Tech oil in anything I intended to keep for any reason.... or similar garbage grade (recycled?) brands
'63 with 390 & lots of juice. But never enough. Always want more.