Squashman, I just replied to your PM. But for other readers, I would say it's a matter of personal preference. I have been experimenting with wider rims which spreads the tires out a bit more and aids in contact to the ground. Also the sidewalls become a bit more vertical and it makes them more rigid. I can run a little lower pressure... Only a pound or 2, but I am able to maintain low rolling resistance as if I had higher pressure. Generally, a wider carbon rim with a narrower tire will weigh in a few grams less. Not much and it's very dependent on the tire carcass design, but it's rotational weight which is expensive to the rider.
Depending on he rider's size, I would go no smaller than 30mm and if running a 2.35, try a 2.25 as an example. a 36-40mm would allow for a 2.1 and you would still have a very similar contact patch. Circumference and cushion from the tire reduces a little, but you will get considerably more contact patch with the wider rim.