I have ALL my jetliners set at 1800 climb, but rarely fly above FL310, unless I'm in the Concorde or Concorde type aircraft or the Gulfstreams.
Through the years, and with the help of folks here, especially Opa, I have learned a few things to make this flight sim business pleasant rather than frustrating.
One little problem that I HAD was air resistance of the aircraft in question.. Opa recommended a program called "FlusiFix-2004 V6.5" which, when used, will correct a lot of these little nagging problems that crop up from time to time. My aircraft climb into the upper Flight Levels now, without any problem and it's seldom that I have to reduce the rate of climb to get there.. This program won't cure all your ills on FS9, but it will cure a lot of them, plus give you some insight as to how files in the program work and what to do to get better performance from your airplanes and the FS9 program itself.
I'm usually here asking for help, and most of the time I get good solid answers that fix my problem, so it feels good to be contributing help, myself..
Never mind the mule, just load the wagon.