Both my 35 and 39 have Columbia's and warmed over flattys so 80 is comfortable to attain - that said - stopping is a MAJOR problem if you have a dire emergency in front of you. Both cars have juice brakes - the 39 stock and the 35 having big Lincoln Bendix units. Even so - a past experience with the 39 traveling at 65-70 when over a hill traffic was at a dead stop in my lane - there was no way my Coupe would ever halt at the rate of modern cars so my only choice was a quick move to the right lane which gave me more room to stop.
I will never forget that feeling of knowing I could not haul that 39 down in time so I drive slower top end even though it is capable of faster speed.