I've use the synthetics and conventional, but only in my trucks. I've never seen much of a difference in either. The synthetic turns black in the 454 same as the conventional. I don't think it makes much difference in the engine.

The only area where I've heard it really matters is in the differential. The conventional is supposed to be bad or at least not as good for limited slip differentials. I don't know how true that is because I've been running plain old gear oil in all my trucks for more than ten years and they've all been limited slip.

Just my nickel