There is a chart which I can't locate showing the height and weight of pro cyclists. There are exceptions like Cadel Evans and others but my recollection was that most were over about 6'. Larger riders would tend to have larger cardiovascular systems and a higher absolute VO2Max. That won't help on climbs where power to weight is the critical factor but for general riding it's the Power to CdA ratio that is important so it depend on who can get into the most aerodynamic position so perhaps tall skinny riders with a smaller frontal area but still large heart and lungs have an advantage.