dave, if you are more on the light side of crewweight, the bim might also be fine. if you are heavier the boyer hulls are surely more solid build.

is it difficult to resell a boat? if not you can buy one now and if you are not satisfied resell it when another boat suits more your demands.

dont know the us market but bim had another mainhook system (a plate with a pin) than the australian and dutch masts. also bending was different.later bims like the javelin do not have the pin any longer. also the beam distances on a bim were different, so basically if you want to put a godall sail on a bim mast you might have to go through some changes...
if bim is popular and there is an active 2nd hand bim sail market, your are not that heavy, I would probably go with the bim. if not, I would try to negotiate a lower price for the boyer. is it a mk3 or still mk2? with the alu mast you might still have an argument to lower the price. if the seller doesn't accept, at least you tried and waiting for a better package might feel a little easier :-)

maybe you can also place a 'wanted' to the a-cat website? some people might think about selling but don't take the initiative to post their boat and don't like to get called by many people but might respond to a specific add.

anyhow good luck!