KSH, what is the course like? Is it flat? Rolling? Hilly? Do your road and TT bikes have the same gearing? What does each bike weigh? There is not as much aero advantage on a hilly course and if you are compromising gearing and/or weight then it might make sense to race your road bike.

Besides terrain, my other consideration would be how much time you've spent training on either bike. Assuming your TT bike has a traditional TT set-up (and your road bike doesn't), it's important to train on that set-up or you'll lose power.

If fluid intake is a concern, ditch the bike computer and get a bar-mount bottle. or mount your computer on the bar or the top tube.

Good luck with your race!!!