I haven’t been riding roads with that kind of speed limits since I’ve had it so I can’t comment on that, but I’m mostly on 35 mph roads where people tend to go around the speed limit. The advertised detection distance is 150 yards, and I’ve had cars that far back detected on straight roads. At 45-50 mph, they’re close to 25 yards a second, so one would have seconds to react. At my current level, I don’t think I’d feel comfortable, but I’m a ham fisted, sausage fingered guy, so take it with a grain of salt.

Gplama has has a video review on the tube site that might be in conditions closer to hat you’re looking for, so if you’d like to watch it I think it might give you a better idea.