Quality Synthetic oil vs Frequent cheaper synthetic oil?

First of all, not all synthetics are the same. Oil change intervals also include the term, "whichever comes first". When you mention 10,000 miles with your AMSOIL option, that probably is connected to six months whichever comes first. Signature Series has a 25,000 miles or one year - 700 hours (whichever comes first) oil change interval - normal service. The second tier option has been upgraded to a 12,000 miles or one year whichever comes first, under normal service use. So you have options that fit your preference.

Pennzoil is absolute crap. You should follow the manufacturers requirement for oil if you want any engine warranty. Obviously AMS oil is NOT the best.

prove that amsoll is a great oil?

you can't, this is just your perception of it

Amsoil isn't any better than Penz. BOTH should be changed in accordance with the manufacturer's recommendations. READ the owner's manual.

Hi so as synthetic oils are better made the normal service period needs to stuck with. nothing is gained from it being one make or any other.

100k without a change? That's not good. I have heard of 25k and thought that was pushing the limit. But 3000 is too soon, especially if it is synthetic. I would say 10k. I would never consider anytrhing else but the cheap pure synthetic. I don't know what else is at stake. Nothing maybe. Amsoil is supposed to have very superior products which is hearsay to me because I have never had an Amsoil product.

Good for you. I just grab whatever high mileage oil is on sale and change it in 3,000 miles.

Change any synthetic at 10K, but I would change the filter every 2500.

How exactly did you determine that the oil was the best?