I went with the 4.5" pulley on the buggy, with the new TC pump from PSC, and it was always fast enough and good at idle. It just gradually quit working as the system heated up with use, and I have a good cooler.
The system on the yellow XJ works good, but is just a touch slow if I need a quick turn at close to idle, and that's with an AGR pump and Tommy Lee box and ram. I think if I go to a 4.5" pulley it will be just right.