A 6m will do fine.
They have a huge windrange!
No they dont, on the contrary...
Almost no windrange...
But HUGE low end, so at least one kitesize bigger than its physical size
Is the initial question, about what size fits an average wind around 25knots, gusting to 40 ?
Or is it about a kite for 25-40 knots wind ?
Around 25knots for 70kg on a TT, you should go for a 7 maybe 8m2.
And if the 2010 Evo, take a 6m2 (which corresponds to a 7-8 in other kites).
Whereas, are you talking about the full range 25 and up (I dont think you can ride in 40 knots), I would go for a 5m2, definitely.
As a 5m2 (older) Evo can be used sweet spot from 28-30 knots and up, at 70kg.
Just my view and experiences
PS: You are correct, if talking in "general" about really small kites.
They have an amazing windrange, compared to bigger kites, even those with less range