I've owned a Jobo CPE2 for over 20 years, bought it new. I have a reasonable working knowledge of that machine and it's limitations.
In Germany when these machines were released, slide processing is what most of these units were purchased for.
The original advertisements I saw, stated that the CPE2 could process 8 rolls of film, which required 1 litre of solution, this was alright for processing one batch and letting the machine rest for another week. But when after a holiday, someone came home and did a developing session over a weekend doing multiple runs, the motors started to burn out.
Before the motors burnt out, and especially if you had the unit full and running on the slow speed, the rotation started to jerk and you could hear the motor straining. Switching to the fast speed immediately fixed this.
Jobo then changed the maximum number of films for the CPE2 to 5 rolls and 600ml of solution and the fast speed.
The later CPE2 machines only had one speed, which was the fast speed.
I am not a trained in sensitometry but I have a reasonable idea of what can and does go wrong when developing film. When the edict for the faster speed for the Jobo came out, I did some tests using my film of the day, I detected no difference in the end result using either the fast or slow rotation speed of my machine.
As I understand it, the slow speed was for film in the 1500 series of small diameter tanks with high volume of solution. The fast speed was for paper in the 2840 type large diameter tanks with low volume of solution. The general idea was that the material being developed spent the same amount of time covered by solution regardless of tank diameter size.
For what it's worth, I have never pre-soaked any film in any Jobo processor and I have done thousands of rolls and quite a few 4x5 sheets of film, C41, E6 and B&W.
Colour paper is another issue with pre-soak. About 18 years ago we experienced a drought and our reservoirs were very low. Right at the end of summer in March I started to get cyan streaks through my EP2 colour prints. I spoke to the Agfa technicians, as I was using Agfa paper and chemicals, they advised to drop the pre-soak and just go straight to first bath.
The reason was that the water authorities add a flocculent to the water to make the solids drop to the bottom. This flocculent was causing the streaks. From that day onwards, I never did a pre-soak for any paper. This could be an issue in the future for quite a few countries as water authorities start to have problems providing fresh water as water usage rises and water levels drop.
Mick.