I answered the question and give some idea of the best and worst case to expect. Yes, I do think I could keep a 34' moving at 6 knots in perfect conditions - that's why I said depending on conditions (that's my silly way of saying not with 2-3' chop and 20 knot winds in your face). I don't know why OP wants to go to NS from RT direct but maybe there is a good reason. Might at least be nice to ask hey, why do you want to do that?

Life involves risks, take some prudent ones (NOT with the BVI ferries)!