I can tell you that I own and drive my own 18 wheeler. Before the big change in emission equipment on big trucks all oils were pretty competitive. After the change, Rotella was the only one that didn't have to change their formula. It's that good!
I've always used Rotella, but I'm considering a change to Delvac 1 this next change (~400mi) in my Powerstroke. What are your applications? I'm interested in seeing if this truck actually does do better in this weather. Are they offering the idea that it'll cold start better and have better idle quality cold or just claiming it'll lube better when cold?
Delvac. I was a firm believer in rotella forever, rotella has taken the ash and other additives out of their oil that made it so good. You can change the oil in a diesel with rotella and in a week you pull the stick and it will be black as the old oil you changed. Delvac looks clean for months. Plus it is cheaper now. But thats just my experience with it. I have changed all my farm equipment, trucks and everything to delvac.
Mobil Delvac MX 15W-40 meets or exceeds the requirements of the following industry and builder specifications:15W-40 API CI-4, CH-4, CF, SL, SJX Caterpillar ECF-2X ACEA E7X Cummins CES 20078 / 20077 / 20076X Renault Trucks RLD
The only reason it has all the good stuff still in it it the title: High Performance Diesel Engine Oil
Otherwise all oils define for normal consumption in normal vehicles have had all the 'good' stuff removed.
When I seen this post it caught my eye, at ambulance service where I work they did a three way study using Delvac (I wanna say 300), Rotella, and Motorcraft Gold cap. Our ambulances idle all day, they are only shut off to be restocked and washed, average around 500 miles in 24 hours. The study came about due to some injector failures in the Fords we had, due to the break-down of oil, parifin in the oil, bleeding past some o-rings into the injectors.
Anyway the Motorcraft and Rotella had less issues, and they have since went to a higher grade of Delvac. For the record the oil, filter, and fuel filters are changed about once a month.
The High Performance title is no different than the Racing Formula designator on Valvoline that allows it to retain its ZDDP. I run the Rotella in my SBC flat tappet driver.