I used a "racing bike" (a scandium Eddy Merckx Team SC) for a 600k and 10 double centuries and a different "racing bike" (a Colnago) for a 400k and 300k. The key really is whether the bike is comfortable for YOU and also whether you have adequate lights and can carry enough stuff. I used an Ortlieb handle bar bag and a Moots Tailgator rack and was able to carry more than I needed each time.