That's a nicely wearing-in engine regardless what oil has gone into it. I take it the suspected Pennzoil was the factory fill oil that you changed out early to flush wear-in, leftover machining, and core sand residual crud? Castrol GTX 10W-30 certainly held up very well, but for the difference in price, I'd consider Havoline 10W-30 or one of the ConocoPhillips synthetic blends in the same viscosity range. TropArtic is nearly a buck cheaper per quart at WalMart. I'm about 2,600 miles into my first run with T/A 10W-30 in my Sonata's 2.7L V6.