Yeah, the sugar content of Coke is probably the least of your worries. Here's the nutritional info for Coca-cola brand soft-drinks:
Coca-Cola Company - SoftDrinkNutrition.pdf
At 4 Coca-cola Classics a day, 145-calories/ea = ~600 calories. In contrast, here's what I had on my last 65-mile **** ride:
300 calories = (1) PB&J sandwich
750 calories = (2) 750ml bottles Cytomax
-----------------
1050 calories TOTAL
or about TWICE what your buddy was getting from his sodas. It's probably not even the sugar, since in your muscles, the glucose is indistinguishable in its source whether it came from a soda, a sports-drink or PB&J sandwich, fig-newtons, or gels.
I suspect your buddy's been training, since speed is more about muscle-efficiency, strength and aerobic conditioning than energy-source. The calories really only determine how far you can go, 60 or 200-miles, but doesn't really contribute much to speed. Or rather, the LACK of calories & sugar will cause you to go slow due to the dreaded bonk.
-------------------------------------------------
Also the typical sugar-spike after a meal does not affect performance, only perceptions in the brain. The insulin-spike in response to increased blood-sugar just moves glucose from the blood into the muscle-cells, EXACTLY where you want it. Just that with low blood-sugar, the brian feels lethargic, but the muscles are primed and ready to go.
Additionally, it's not possible to get get a sugar-spike and drop while exercising. The limited digestion/absorption rate of 200-250cal/hr cannot keep up with the burn-rate while exercising. Even if you were to gulp down all four sodas while riding, they will only be absorbed at this low rate. Meanwhile, you're burning off 500 calories/hr while riding and your blood-sugar continually drops during the ride. That's why on long rides, you need to back off the pace so that your body can digested food contributes a larger percentage of the calories burnt. Burning off glucose at a 400 cal/hr pace will let you go much further than a 500 cal/hr pace.