Honestly, the best performance I ever had in my life was on a 50km race a few months after finishing a 2700 mile MTB race. Safe to say the 2700 had a lot of long, slow miles. That massive base (and recovery afterwards) allowed me to win the 50km race, by 10 minutes, against Cat 1+2 and one pro (who got second). Also everyone else had more than one gears on their bikes.