I've found several other questions on here that answer, "what's different between synthetic oil and regular oil?" or "Can I use X oil in Y car?", or similar, but nothing that quite answers my question.
I have a car with a high revving engine that requires 10w-30 full synthetic oil. My mechanic (who primarily works on racecars) uses Valvoline, but several other people I've talked to swear up and down that if I'm not using Mobile 1 or Royal Purple or insert-your-favorite-brand-here, that my engine isn't going to last as long or perform as well. When I'd ask about the difference though (they're all 10w-30 full synthetic, right?) none of them could give me an answer. I'm aware that certain synthetics might be parafin based which would gunk up the works, but I don't think any of the above examples are actually parafin based.
TL;DR: Is there really a difference between different brands of full-synthetic 10w-30 oil?