first of all..BLOODY AWESOME KITES
I weigh about 65kg and ride the 11 2004 matrix on a 122 flx and 15m lines...get planing a bit below 15 knots and can hold it down up to about 25 knots but anything beyond that is not fun.
Its a bit hard with the sizing because initially I wanted a 10m as well (came from a gaastra force 10)...so decided the 11 would be better. If you go the 11, you may want to consider getting a smaller kite for strong wind days (looking for one myself) but if you go the 8.5 you may find that you dont have enough power for the lighter days. The last few days have been pretty gnarly so you may want to weigh out your options.
IMO go the 11 for the average seabreeze.
If you see me at the beach, give me a yell and you can have a go.

I have the 05 16.5m and the 04 11m so its a bit hard to comment on the smaller sizes of the 05 kites.
They are grunty kites but Ive had little if any trouble in gusty conditions. Unhooking in the strong seabreezes (above 20 knots) can give you a bit of a work out but I suppose that happens with all kites. Nevertheless it hasnt given me a problem athough Ive developed a case of frozen shoulder from too much unhooking in strong winds. Looping is awesome but not as fast as rhino 04...05 matrix is supposedly faster?? cls is really good although after a few sessions the hassle of the extra line makes you think if its really worth it....besides which you would almost never need it for relaunching because they relaunch very easily. Ive used a couple of times only for depowering th kite when overpowered on the 16.5 (just pull it in a foot or so).