David,
That is a nice motor but probably not best for this application. The high kV number means it will want to spin whatever prop you install at pretty extreme speeds. On a small prop, that's no issue, but for this setup the nose of the BB will eat most of the prop wash, wasting your thrust. Most airframes using this motor will be pushers (no fuesalage eating thrust) or airframes with narrow, streamlined noses.
That being said, *** if you must use this motor *** HK specs a 5x5 prop, and several commenters say they're running larger props, but nothing near an 8x6. ecalc will also assume that you're flying WOT(wide open throttle). You could easily use the 5x5, but only go WOT if you need it.
Fly a short flight and see if the motor has gotten hot (not just warm). If it is, under-propping the motor won't help -- replace it now before you burn it out and can't use it on another airframe. You'll want to get a slower motor with a longer prop for that airframe, and save this for something like a Versa or FT22.