I ran 28 psi front 30 rear on an MC21 with std wheels. Most would run 30/32 to start
You will need to drop them a lot from the standard road pressures to get the tyres to work.
GPR's were great and seemed to last quite well.
- 10 year old Japanese Bridgestones were 'interesting' at a cold wet Oulton Park. I got down to 25/27 which was better if a tad squirrely, but still not getting hot enough. (I weighed only 8 and a half stone at the time - better now).
Mike