I am 67kg and i have used 7m M5 (2010) in 40knots gust. it was not comfortable and the snow was super hard. But it's not best choice to do that... it was only to test the real limit of the kite for a competition.
so for the strong winds it's depend a little bit what do you have like quiver...
the good combination are :
12.5 - 7 montana
or 9.5 montana - 5 apexIII
if you have the option to have 3 kites it will be still different.
it's so difficult to help people to choice the right wing... it's so depending to the skill, spot, snow condition, snowboard/ski and personal interest.
i can say 7m M6 it holds 30-35knots full trimmed and not using powerzone at all