Greg,
I had a 19p (cupped to 20) stainless on my 211 when I had the 460 KC installed.
You can easily "ballpark" your props by using the following prop-slip calculator.
http://www.go-fast.com/Prop_Slip_Calculator.htmA single prop (drive) boat would exhibit about 12-15% slip as a rule of thumb (when planing at medium to high speed) for calculations but if you have verified your tachs and are using GPS you can calculate your slip (which should be less since you have 2 drives)
If I remember correctly ALL the drives behind the 460's are 1.41:1 ratio.
I used to get about 60mph at 5000 RPM using a 20P (19 cupped) prop.
With the 454/Bravo III I now get 57mph at 4600, 1.81:1 drive and 26p props (8% slip)
I think with twin drives you might be in the 10-12% (or even lower) slip area but you'd have to measure your speed and RPM accurately to know for sure. (twin counter-rotating props might even be about the same slip as with twin drives.)
Enter the prop-slip calculator with your gear-ratio, pitch and RPM. click CALCULATE under "Theoretical Speed". That will give you the speed you would get if there was NO slip (which is impossible )
Then if you know your actual speed (using GPS or other accurate method like RADAR etc) you can put it in the "ACTUAL SPEED" field and press CALCULATE under the "SLIP" field and it will give you your slip.
Regards,
Rick