Some of us have started using Rotella synthetic, including Dave and myself, because it was attractively priced. However, if you look into the details of the oil, and I won't go into it here, the Rotella is a Group III synthetic that is not up to the performance level of the Mobil 1 which is a group IV synthetic.

Now, whether you really need a group IV synthetic is a different story altogether. The group IV oils will typically allow you to go further between oil changes. However, with your engine, this may not be possible in any case due to the amount of soot that it produces.

I will probably continue to use the Rotella in the 617 because I will definitely change it every 5K. Now, the 603 can probably go longer than 5K, and, it has lifter noise, so I will likely switch it to the more costly Mobil 1.