People make this comparison all the time but I think it's myopic. If you can get into the same position on two bikes but one is more aero than the other, why not get the more aero one? It's not always about going faster at the same power, quite often (especially for "endurance" bikes) it's about going at the same speed more easily. There are lots of times when I've been fighting a headwind on the way home at the end of a long ride, and at that point I'm pretty happy to get whatever little benefit I can, even if it's only 4 or 5 watts. Likewise, even if you're cruising along way below your FTP, talking with your friends, after five hours of cruising there's a difference between having averaged 60 watts or 64 watts below your FTP. Aero can mean faster, but it can also mean easier.