thanks for the advice.
a couple follow up questions:
1) realistically, can one use a 8.5 sail on the FU 122 comfortably? Having a FU 122 and later a smaller used board would be more attractive than a three board solution, however I've been extremely happy and comfortable with my Carve 145 in light winds with a 7.0 and 8.5 Retro. I wouldn't want to have to struggle with a 8.5 on a 122 liter.
2) can a FU 111 realistically handle a 5.0 sail? If so I could comfortably sail it 5.0 to 7.0 and keep the carve for 7.0 and 8.5