Ever sail an Apollo?
That was the early planing king!
I agree with some of what you say, an older smaller Formula board (ala F-155) would be very good,
But I see some real issues jumping from a 5.5 m2 rig to a 10 m2 plus modern formula rig with
550 masts and huge heavy booms on a 2010 and later full formula race board.
I was looking at a progression.....
Also, rgomez (the OP) was looking for something that planes in the 5-10 knot range.
I think we both have enough experience to say that no one planes in < 7-8 knots, even with a huge
=> 10m+ sail and the very best technique.
I will stick with my opinion that a modern full on formula board (even a beat up used one) is still going to be fragile, hard to get planing with smaller rigs and fins, so it's not optimum as a progression board from
the Funster 180.