Good points everyone, but shkval wants a board that will get planing the soonest.
I agree with all of you that in < 7-8 knots, the formula board isn't going to plane
(at least not easily) and on his Tennesse lake there are for sure to be lots
of holes, so he's going to come off plane whenever the wind drops below about 8
Also, as it was suggested, he's not racing.
Comparing what racers do (upwind/downwind alot) to what recreational (B&F on beam reaches)
do does not make much sense to me.
A big sail (but I would caution against a big "full race" multi cambered sail) will help, and there are
lots of really good Free Race (both cambered and camless) sails on the market that have exceptional
low wind grunt and can be rigged very full without all the loose leech stuff at the top and still work/rotate
An Apollo would be perhaps the best, then a full on formula board, with a Free formula 138/158 (not the go based FF) right in the running.
Wider is pehaps better here.
Planing some of the time, in B&F beam reach recreational sailing, is still more exciting, even with pumping to get going, than the same sort of sailing on a longboard, IMHO. Been there, done both.
Racing @ < 8 knots..... longboard for sure!...... B&Fing at > 7 knots.... Planing some could be
alot more fun.
Hope this helps,