What prop should i buy for my f115?

looking to upgrade my prop from the stock propeller my yammi came with. The stock one is a Michigan wheel prop 992116 "12.75x21"

I noticed it aluminum and has some flex on the blade. I'm looking to purchase a stainless steel prop that can give me a little more top speed. What would you suggest me buying?

Any info would be greatly apprieciated....TY http://www.bassboatcentral.com/smileys/USA1.gif

mine came with a 19K .. been wanting to try a 21