Little Prop Help Please

[csvencer]

I have a 14' McKee (it's not as nice as some others on here may have....but if floats) that I just put a 50 HP Johnson on. Right now it has an aluminum 11.75x17 prop and wide open she is hitting 6000RPMs. The boat is light right now (just dropped it in for a test ride) and the prop has a couple of dings. I was thinking I would need a 11.75x19 or even 21 to get me down to 5500 but I can only find 12x17 props. Think that will drop it down enough? I am sure the dings and the fact that it's aluminum and flexes, my 6000 may be bumped up a 100-200 artificially, but I just don't think adding a .25" to the diameter is going to get me down the other 3-400 RPMs.

Thoughts?

-Svence