I think this comes down to how much comfort you require. Race bikes are comfortable over long distances, but other bikes may be more comfortable, for various reasons.
It is a compromise between how much comfort you want, vs other factors. But because there are more comfortable bikes out there, doesn't mean race bikes are uncomfortable and a race geometry road bike may be absolutely fine for the OP and may prove to be the best choice for subsequent use following this event. Or it may not, depending on the degree of comfort he wants vs other priorities and future plans etc.