what's the difference?

[nitrostarter]

Well the problem is gearing. You are pretty much maxxed out on your gear ratio as of now with the 2200kv motor and you are able to push it. If you can get a larger pinion gear, like the ones from spd-si or whatever it is, then going to the 9s 1.5Y(1500kv) will be in your favor and allow you to turn those larger gears at the same motor RPM.

Then again, there's also the theory that the motor rpm number you are posting are just that, theory. They theoritically should turn that many RPM, UNLOADED tho. Throwing a load on and factoring in drag and aerodynamics, you may only be turning 50,000 rpms right now. Switching to the 9s setup will have even more power and efficiency thus allowing you to push the full 56,000rpms.