In regards to the max speed, it's true that in a worst case scenario, winter tires tend to be Q-speed rated, good to about 99 mph. But, with the studdable and "high end studless", tires, if you have to do an emergency lane change, and you were doing say 90 mph at that time, slamming the brakes and performing evasive maneuvers may still lead to a crash, since the tread tends to be very squirmy due to the design of being more heavily siped for that snow and ice traction. Mazda's arbitrary recommendation is probably based on braking and cornering at the same time without killing yourself. If you have a "performance winter tire" that can be H or V-rated, you can drive a little faster, since the tradeoff for better dry road handling is worse snow & ice traction. But.. what if you're driving through say Utah and you're in a 80 mph zone on I-15? Drive slower and stay in the right lane unless you need to pass someone. It's a speed limit, not minimum speed. Some highways may have additional signage that indicates minimum speed, but that tends to be around 45 mph, if you're driving that slow, your hazards better be on.