Conventional vs Synthetic Oil Debate

I was raised on "3000 miles, change the oil and filter " like many of y'all probably were. The 90 R2500 Burb I had, that old truck had close to 300 thou on the original 350 TBI motor. When I pulled the oil pan down (because my dad thought the timing chain broke-- nope, still fine!) the last time I was under the truck, the cylinder bores still looked pretty good. Quaker State 30W,and a new AC filter, every 3500/4000 miles. And this was before the "high mileage vehicle " formulation. Didn't leak or use any oil either.
On my other 99 vortec 5.7 Burb, QS 10w30 like GM recommended, AC PF1218 filter. Aimed for every 3500, but often the other side of 4000. Did timing job and pulled the oil pan down, could still see cross hatching in the bores at 175 thou. No telling what kind of maintenance it received (or didn't) from previous owner/s. Bought both trucks used, as all our Burbs were. Use QS 10w40 high mileage formula in the current Burb, and a PF1218 filter. The AC is recommended for the vortec because it has the anti drainback valve, which many aftermarket parts don't have. Probably more needed on the 4x4 models since the filter is horizontal on them. I used to be able to get the filter at Walmart until they decided to quit stocking parts for 20 years old trucks LOL. Now I get them from o'Reilly for around 6 bucks.

Valvoline VR-1 Racing is a very good oil with a decent ZDDP level and additive package.