That's "moot" point.

If the frame geometry between the bikes is very different, I wouldn't race the new bike until I had ridden it at least a couple of times to dial in the fit and get used to the handling, and also to make sure all the mechanical adjustments were properly done. The last thing you need in a race is to have a cable stretch or a handlebar slip or crank come loose. The general rule of thumb is to never make any major mechanical adjustments before a race without having an opportunity to thoroughly test and re-adjust as needed.

(BTW, I race bikes. I have a "training" bike that is more comfortable, especially for longer training rides. And I have a "racing" bike with more aggressive geometry. The week of a race, I make sure to get in 20 or 30 miles on my racing bike just to make sure that I'm comfortable with the different feel and handling.)

More important than which bike to ride is the fact that you said you've never ridden in a peloton. You absolutely need to get in some group rides before your race. Training solo is like driving your car on a deserted highway. Racing is like driving your car on a busy freeway. No matter how skilled a driver you are, if you've never actually driven in traffic before, you're in for a big surprise. Actually, this analogy is still off the mark, because there is a quantum leap between riding in a group, and racing in a group.

For your sake, and for the sake of those around you, get in some group rides before your race.

Of course, we'll want to read your "Race Report" after you've finished.

Good luck!

Bob