No clue what type plane you're working on, so I'll just go on the fact I don't like more than 8" of pitch as a rule (fly mostly acrobatic) and my WAG will use that pitch. To drop your rpm 2K or so, you'll need to increase your prop diameter by a couple inches, to let's say 17". Now, you can convert that 17x8 2 blade that should turn somewhere around 10k, to 3 blade as you wish. Probably a 16x8? Again, all purely hypothetical. Your results probably WILL vary, but you should be a LOT closer than you are now....