In my 04 RK custom I run about 10 pounds when I ride by myself. I am at 230 pounds and that gives me a nice comfortable ride. If the wife is with me I usually run about 18 to 20 pounds. Anything more then that and a bump in the road will give me a pretty good jolt.
with my streetglide, i used what was recommended in the owners manual. between 5 and 10 psi. hit some potholes, and found out from other sg owners that 20 psi for my 200# of bodyweight would be right. this was great. i run it at 20 now. the streetglides have a shorter shock and need more air than the longer roadglide and electraglides. no longer does the suspension bottom out. i hope this helps. check with other riders who are riding a similar bike as yours is the best suggestion i can give.
Changed the oil in them yesterday and have them at 14 psi riding 2-up. A couple of roads that we ride have some dips that would normally bottom the shocks out with 20 psi. Today no bottoming, no jolt, just cruised right on thru. '08 RG