Single handed on the 17 I'd say things start getting silly at around 30-35 kts - Kite goes up, but I don't gybe as there is usually too much happening!

2 up I've been out in about 40 kts in the Hurricane 59 but we were both VERY experienced.

Both on an inland lake approx 3 miles by 1 1/2 with excellent (and I mean probably the best in the UK) saftey cover.

Was 30+ with the kite up fun - well some of the time I suppose.