BB, I've been looking at the same two oils for quite awhile. I've always used Rotella-T syn and have always eyed Mobil1. There is no question that Mobil 1 is the "better" oil.

However, I change the oil on them every 5K because I don't want to accumulate more than 1% soot. My feelings are that soot is abrasive and I don't feel comfortable pushing the numbers up toward 2%. So, it doesn't make a whole lot of sense to purchase the Mobil1 if I only go 5K. Now, I'm tempted to push the OCI up to 7.5K with Mobil 1, but, only if I can get it for $4.00 per quart. If I have to pay $4.78 per quart, I'll just stay with the Rotella-T at $3.25 per quart.

I'm also disinclined to go to the Mobil-1 because I consume 10 quarts in 5K OCI (burns/leaks 2 quarts).

The oil analysis of my 603 had been quite good for wear metals over the last 10K and two oil changes.

http://www.peachparts.com/shopforum/showthread.php?t=115381&page=2&pp=20&highlight=Blackstone