we have a local tt which is a 8 mile out and back tt. The record is 30.5 or 31 mph. I've only ever broken 29, but the out has two climbs, and i'm a fatty
(this is with full tt gear on my tt bike)
Then we had (wish we still had) a prologue tt that was just awesome! it was maybe 9 miles total, and the winner of the p/1/2 race was always north of 30. I hit 28.x in it last year (#imslow)
I did a 11 mile tt the other day on my road bike for another local tt series, and hit 26.9, but it's relatively flat (one small climb at the beginning, and a short descent before the final turn back to the finish).
But to put things in even better perspective. the 29 mph tt was at something like 330-340 watts, where as my 10 mile tt was north of 360 watts because i was on my road bike, without aero gear (I'm not that aero even on my tt bike).