Ken Cox has some good points! It's all about how much work gets done in a given time span, or how long it takes to do a given volume of work = power [work/time]. If you're a "power" rider, you won't need the geared bike as much on hills or in a headwind. If it's all LSD, you may do better on the geared bike. Comparing riders is likely more valid than comparing the type of bike they ride.