If what your really want is a board that's good in 10-15 knots, then yes, the Is 122;
Futura 144/155 make sense.
If you want a board for < 10 knots, then look at the wider FT 138/148.
The F-Types were fairly fast in the light winds because they light up early and the width helps carry them through lulls.
The narrower the board, the more the lulls are likely to affect it.
Once you get to 12 knots then of course the IS 122 is going to be the fastest.
How much faster....... maybe 2-3 knots on the top end vs the Futura 122, maybe
4-6 knots faster than the F-Types, but not at the lower end of the wind spectrum.
It's a tough decision I know, and I almost don't want to make such subjective comments because your sails/skills/conditions could easily "skew" what I suggest either for better or for worse.
Hope this helps,