WOW! Great discussion.
I can't really speak to your situation or give you advice... other than... go with what you feel good on.
Now, I have to say, IMAZ is pretty flat and can be windy. A tri bike or at least some aero bars will be beneficial there.
I have a Cervelo One (older model tri bike)... and a Specialized Tarmac roadie.
I am going IMKY in August... and I have decided to ride my road bike there. I'm comfortable on it. I really don't see why I would take a tri bike on a hilly course. So thanks Silver for saying you road the course and you think a roadie would be great on the course.
My road bike is the better climbing bike. So you have made me feel good about taking it to Kentucky. I know I'm going to be the dork on a road bike, but screw 'em. I'll be happy.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"