Nothing to do with speed. All depends how close you are to the vehicles in front.
Not strictly true. Whether you get hit by a stone thrown up by the car in front depends on whether the stone falls below your car before you get to it. The faster you're going, the sooner you'll get there & the greater the likelihood of hitting it for a given fixed following distance. Also, and importantly, the faster you're going, the more damage it will do if you do hit it. I'd suggest hitting a stone at 70mph is about twice as likely to damage the paint as hitting the same stone at 50mph.
That said, I'd agree the best way to mitigate the impact of stone damage (pun intended