May I assume that Simon A. is Kitesurf as well?
1. I know of a Redbay Stormforce 11 (Awesome Explorer owned by Andy Micklewright) which has twin Yanmar 300's with Bravo 3 legs which suits it ideally and which presumably will fit your application well. I am told that jet drives "lose" 20-30% of their power in driving the waterjet, but are ideal for amazingly close manouvering like entering caves for example. So if going this route you might want to select a larger engine. Several around at about 450hp.
Still, Bay of Biscay? two engines?
2. On your kiting foray. At least 3 large ribs (maybe 4) will be returning via the Scillies from S. Ireland on the weekend of the 22/23rd May. See
and S/W Ireland page for details, if that ties in at all with your schedule.