I can see now from 3d graph - 10/20 Kms test cannot be done unless you use a boat or go straight across the bay,
Let us know how the Xr5 compare to the R5h,
Also i use nstreame and i find it good and a lot of positives by other posters on the forum using ptp links,
And as you are transmitting over water, perhaps a read of this topic might be of interest ?
http://forum.mikrotik.com/t/automatically-change-frequencies-to-compensate-for-weather/28267/1
must call down, ky is a lovely county on a good day,
n21roadie