Just out of my curiousity, have you ever tried mobil1?
Maybe it would be interesting to do a poll on this.
Let's see here;
1. Mobil 1 and a new filter every 3k miles
or
2. Amsoil and a new filter every how many miles? 25K miles you say.
Don't poll that or you will get laughed out of town, I suspect.
Just kidding, but seriously, Virtually all of the high dollar auto manufacturers reccomend/require Mobil1.
Recommended/required for all new vettes, and maybe all GM.
Recommended/required as a minimum for all new BMWS, but I think that they would like for you to buy their own brand oil at about $ 16 a quart, I believe.
General motors (what do they know) has such a strong conviction regarding it that they have extended their minimum time/mileage intervals for maintainance when Mobil1 is used.
So, Amsoil might be better, at 2x the price, and you are going to trust it for how many miles?
I have run Mobil1 since about '86 through a Guldstrand/Traco '86 Grans Sport 80, and 5 turbro regals, and its also run in my new, or almost new Z06. I have never had a problem that I can attribute to oil. I have also never lost a turbo, either, out of 5 turbo cars. Sorry for the long post.