Rotella users: T4 or T6?

[ChickenPinz]

I've moved over to the Rotella camp, using T4 15W40. I'm contemplating T6 for the next change, and am wondering what others, who are using Rotella, ended up with and why?

The T6 is more expensive ($23 vs. $16/gal), but cost isn't a factor given TCO. Anyone see a downside with the T6 vs. the T4?

[whitesik]

I have always used T4 as recommended by the previous owner who was a Porsche tech at one time working on a lot of air cooled engines. I've got nothing else.

[Jim LaGuardia]

Use only 30wt per operating instructions.
Rotella T-1 30wt with a bottle of STP with ZDDP additives.
I see firsthand what damage thinner oils do.
If you want it to last, use the right oils.
Thin oils are quickly consumed through valve guides and also cause piston scuffing.

[whitesik]

OK Jim, Bought some Rotella T1 straight 30 today. Thanks!

[ChickenPinz]

I conduct oil analysis with Blackstone for most of my vehicles. It's $35 of value/entertainment.

Here's what they came back with most recently:

As you might imagine, we haven't seen many samples from these air-cooled 2.5L Steyer-Puch
engines over the years, and this is the first one where the interval on the oil was recorded in hours (34 hours).
Universal averages are based on ~3,500 miles of oil use, though, and it's nice to see most of the wear
metals in your sample reading lower than averages after what must have been a shorter oil change interval.
Chrome is the exception, and it comes from piston rings. If the rate of oil loss is stable, check back next oil
change to start building trends. No contamination was found.

The Chromium number was 4, vs. the "universal average" of 2. This batch was with Castrol 20W50 High Mileage, and the Zinc number was 637. They did not report any antifreeze contamination.

I'm on Rotella now....we'll see how the numbers come out in the future.