Whoa, let me get on first; the answer to your question is dependant on the following:
1) type of kite (LEI or Foil)
2) Your weight
3) Type and size of board
4) Location (a warm northerly in QLD packs less punch than a cold Southerly in Vic or WA)
Cabrinha convert 9m. Cabrinha switchblade 12 m. Underground twin tip flx152x42. 74 kgs. Newcastle area
Cabrinha convert 9m. Cabrinha switchblade 12 m. Underground twin tip flx152x42. 74 kgs. Newcastle area
Switchblade has plenty low end grunt but is quite heavy so I reckon your "ideal" window would be 14 to 20 knots on the 12m and 17 to 25 knots on the 9m.