I come from the position that on a dry, well-maintained, and straight road, with no traffic, I think even 100 mph is a safe speed. I assume people like you that even consider 80 mph to be unsafe are assuming there's significant traffic on curved roads that might not have the best maintenance. I also assume you're driving a large truck or SUV which has abysmal handling, whereas I'm used to the tighter handling of my Subaru BRZ.
Generally, I don't think speed causes crashes, it just makes crashes worse. So if I'm coming from assumptions above, then crashes basically won't happen.
Add some traffic? Then the safe speed depends on their discipline. Are drivers keeping right except when passing? Or is some asshole playing "traffic cop" and camping the left lane at the speed limit, or even below it?