"faster = farther" only works for the "short" long-distance events (like a century or 200K). At some distance, even at Olympic speeds, you're going to be on the bike for a _long_ time. Even if you could average 20 mph, and not sleep, a 600K is going to take 18 hours. So eventually, if you get hooked on long-distance riding, no matter how fast you go, you have to have a bike that fits you well, which also means a saddle that fits you well, and a position on the bike that is comfortable for hours on end. This helps you to ride fast, too. I never did any sort of structured training during my first two years of brevets; just commuting to work and riding brevets and centuries. So my view is that while speed work and intervals and hill work are all great for helping you finish the ride faster and stronger, they're neither necessary nor sufficient for riding long rides. But having a bike that fits in every respect is a necessary condition for being able to finish long rides.