iSonic 133 or 122 ???

[hubert]

I'm 30, weight 80kg, 179 cm, sail for 3 years.

current gear:
JP Xcite ride 150, Severne SSR (2003) 8.5m, NP V8 7.5, Mauisail Pursuit 6.0m

status:
footstrap ok, learning jibes and I'm almost there (to complete a jibe, not with good exit speed)

environment:
10~15 knots most of the time, flat water in summer, lil 1/2 mast height wave in winter.

I'm thinking to get the iSonic as my second step board. my friend is riding a 122L iSonic, and he said the board is amazing with most of the volume on the back of the board, which makes the board feel like a 130L board with a lot of float. (he is a really light weight sailor, 60kg, 5.5ft tall).

here's my questions:

*should I get 133L or 122L?
*the 122L is longer than 133L, the homepage mentioned the 122L got better fin drive and improved release (frankly I have no idea what that is), does it matter?
*does the above matters (length, the fin drive thing) affects the speed?
*should I understand that 122L and 133L is a different design? how does it work?

thanks for your help!!! ^^; I wish there would be a 128L iSonic in 2008....

CHEERS
Hubert