I've done the not recommended 75 with stuff on my roof and the thing will not move. I can shake the car with the rack and it doesn't leave any mark. If you make proper measurements it will fit perfect and you'll never have a problem. Either way you go, Wax your car first before putting it on to give it an extra layer of protection. It still won't move on you. I think it would rip my roof off before scooting on me. I trust the hell out of it. I humored putting a 4x8 sheet of plywood up there because I don't have a truck and needed some sub-flooring. Only reason I didn't was I didn't want my car to take flight. It's gracy to put on and easy to take off. Literally takes about 2 minutes for me to put it together and most of that time is spent walking around to the other side of the car. You can't go wrong with either but I would say that anyone who had the rack slide on them didn't measure the width of the towers correctly. It's not supposed to fit loose.
Also, you can put any accessory on a yakima - thule or yakima or sportrack (made by thule) or black widow - whatever. Not sure about the same with Thule. It might be so.