about 6 or 7 miles until my paranoia of blowing out a tire got the best of me. :-) Then we slowed to a much more reasonable 110mph. :-) Couldn't even hear the wind noise then. The Z is a great high speed cruising vehicle.
This was in the good old days when Montana did not have a set speed limit - only "reasonable and prudent" in the day time. Since traffic was almost non existent along the stretch of road we were traveling on (at one point we traveled 62 miles without seeing a soul), "reasonable and prudent "was whatever speed you felt comfortable driving. Good times.