Zephyr11

Keep in mind there's more that goes into it besides total weight of the bike. For example, rotating mass counts for more than non-rotating mass (wheels count for more than frame, rims count for more than hubs, etc). Geometry will also play a role, since some bikes will put you in a more aggressive position that might enable you to generate more power. Finally, as silly as this sounds, there's the mental aspect. You said you're a marathon runner...you know how you run faster in flats than trainers, even though the weight difference is really small and should only account for a few seconds per mile? Yet the difference is significant just because you *feel* faster? I ride better on my squishy than my hardtail, with more of a difference than rear suspension should be accounting for, just because I *feel* like I'm more capable a rider on it. Buy a bike that feels fast, and you'll be faster.