Max TAS can be reached at FL410 and certainly at 370...if one pushes the airplane. However, there's no need. It cruises quite comfortably at 370 KTAS. While Piaggio claims faster for advertising purposes, realistically it's 20-30 knots slower in cruise. And it's quite comfortable at FL410...I've spent plenty of time there myself in the P.180.
However, It's really an issue of whether Mmo can be reached at altitude, rather than max TAS, isn't it?
Regardless, the airplane has no tuck or flutter tendencies. Flutter isn't an issue as altitude increases, and the airplane operates at a low mach number.
Piaggio insists the forward wing is just that: a forward wing, and insists it's not a canard. I originally underwent factory training by the factory chief pilot...and that point was made repeatedly.