Jags,
This is what I think my ranges are:
Board: Airush Switch 142 x 40.5
Rhino4 18 range 12/13-19 Kts sweetspot 14-17 Kts;
Flexifoil storm III 15 range 15-27 kts sweetspot 17-22 Kts;
Wipika AirBlast 2002 12 (old 8.4) 19-28 Kts sweetspot 22-26;
Change boards above 22Kts to Airush compact 133 x 36 as the compact is more comfortable and holds more power:
Wipika Airblast 2002 12 24-30+ Kts sweetspot 24-28 Kts.
These are all 4 line high aspect kites which I like but these Ranges are, I suspect quite different for med. aspect kites and 5th liners. You got to try them out.
Hope this helps.