For a closed course its much more about how long can you hold a set cadence than speed. If its an open or turn-filled course spped matters a bit more. Any info on the route, PedallingATX.

And if you want to have even more info to dork out over. FixedGearFever(the best track racing forum/site around) has a gear calculator that figures in average speeds and times including a standing start. The other one listed assumes a set cadence/speed with no change(such as accelerating up to speed. Its here http://www.fixedgearfever.com/module...download&cid=1 then download The Ultimate Gear Spreadsheet