I'm running on my 6th gallon on my OS 15 cv-r(x). It still is a screamer with plenty of compression and power.
For life of engine it's about 10% engine type, 10% engine manufacturer and 80% user that dictates an engines life. If you don't run to lean, you don't over heat, you don't over rev, you run clean fuel filters, clean air filters and just a generally clean engine, you will get a long life out of it.
It's just like anything else. If you take care of it, it will last. If you don't, then it won't.