Cat 6 going on PRO....
Just taking rider/bike weight into account to start, that is going to save you about 4 seconds on the course...
5% decrease in total (bike + rider) aero drag would save you a further 1.5 seconds... (probably very optimistic if your riding position is the same).
The fatigue/power part is difficult to gauge... 10% more average power is going to save you a further 7 seconds...
That cuts 12.5 seconds off your time.... that's assuming the wind is the same.... make sure you do the course with the wind at your back and it'll help...
If you can tell me your current best 2 minute mean maximum power we could use that to determine how much more power you can develop when you are fresh and get a better estimate....
http://www.cycle-speed.com -Online Cycling Marginal Gains Calculator
No. I do not deny it.
You are comparing two bikes that have substantial weight differences. In my comparisons, I am comparing the extremes of my current bikes which range from ~17 to ~22 pounds.
Ironically I had a 1976 Schwinn Varsity up until this summer. I didn't bother with a cyclocomputer on it or take it on any serious rides. I had to thin my bike herd since I had added an additional motorcycle to my collection. On flat rides, I could probably keep up with anyone I could on a lighter bike.
I am riding a 20 pound modern road bike because the incremental difference in efficiency is FAR greater than the comparison on a ~20 pound bike compared to a ~15 pound one. I am just as capable and competitive on an entry level road bike as I am on a $2000 bike that is x pounds lighter. None of my bikes are equipped with anything better than Shimano 105... In my last race which was a crit I placed 2nd. The outcome had nothing to do with bikes. Everyone was on modern road bikes ~20 pounds or under. Tactics and bike handling played a much greater role in the outcome than a few pounds of bike material did.
Again, I am not disputing that a lighter more expensive bike can possibly give you an advantage. I am just disputing the actual amount which is nearly zero in my opinion. You could also have a lighter more expensive bike that has more relaxed geometry and it is then "slower" than a heavier bike that has the rider in a more aero position... To sum it up when comparing modern road bikes...it's not the bike. Engine and aerodynamics.
I guess the op has to decide that winning the sprint to the stop sign on his A ride is worth the very large outlay of cash for a flash bike.
I honestly don't think it matters a whole lot, especially when we are talking about group rides.
That thread from roadbikereview that was posted a little bit back was very telling.
"Even people opposed to religion need calm minds and compassion to make their work more effective."
I'll confide in you guys, I got the 15 pound S-works because of it's obscenely light weight. Does it make me any faster, sure incrementally, mainly it's a lot easier to carry then a 25 pound bike when I breakdown a zillion miles from anywhere!
With that said, of course the differences are very, very small. But in bike racing, fractions of a second are often the difference between winning and losing. So small differences in equipment matter there. The question is whether we think it's worth paying for those differences. And the changes in equipment that make the most difference might not necessarily be about what's lighter or more aerodynamic, to be fair. The switch from downtube shifters to integrated shifters is a perfect example. Even holding weight the same, being able to shift immediately, while under full power if desired, is going to make you faster. Not a lot faster, but enough to matter sometimes.
Outside of bike racing, of course there's nothing at stake, but the differences are still there. Some people like the idea of being on the best, fastest stuff they can get their hands on, even if it will never make a competitive difference for them. Nothing wrong with that.
I just think that both extremes of this argument are stupid. It's stupid to think that getting a flashy new bike is actually going to make you lots faster. But it's also stupid to deny that differences in equipment matter. They definitely do! Even if it's just in how warm and fuzzy we feel about riding.