Although, I think most FH throws are speed dominant and have a relatively low ratio of spin to speed compared to BH. This causes the disc thrown FH to act more understable so the more overstable discs are thrown. Take for instance Ricky Wysocki and Jeremy Koling. Both have good OAT free forehand throws but Jeremy uses understable discs because he gets a lot of spin on his throws because he keeps the elbow close to his body and gets a good wrist snap. Ricky on the other hand, throws like a sidearm baseball throw and develops a lot of speed on his discs with a lower ratio of spin to speed. This is why Ricky tends to throw overstable discs like firebirds.
Also, I agree with Martin that if you are learning to throw FH (or BH for that matter), learn to throw neutral mids and putters like ions, aviars, and comets. If you can throw these 250-300' flat and have them go dead straight then you have pretty solid form with very little or no OAT.