I don't remember reading anything about speed restrictions. I had it installed at fun and sun though so I really didn't read much of the paperwork. ALWAYS use front and rear strap downs. I also load my kayak upside down which seems to help with dynamics.

I've owned Thule and will never buy their products again. Rack broke and they did not stand behind their product. Yak did a nice flip down the highway at normal Texas driving speed..lol... over 50mph that's for sure.

Go with Yakima.

If you are that worried about it you might see if having a trailer hitch kit installed (yes they make them for cars) and finding a cheap trailer would be a safer and easier option? I was going to go that route on my fusion after using a roof rack for about a year or so. It gets tough loading a kayak on and off your roof especially at the end of a long day when you are nice and wore out. My solution was I gave my wife my Fusion and bought a Ranger so I could just toss my kayak in the bed of the truck and be done with it lol