Originally Posted by boyze
frame - 2%, wheels - 5%, components - 1%, legs and lungs - 70%, race tactics - 20%, luck 2%
This is also my call. I drop roadies on fancy bikes when I'm on my steel touring bike with panniers all the time.
Having said that, the bike does make a difference. My racing bike is definitely faster than the touring bike. Sprinting at 30+ on the racing bike on level ground with no wind assist is quite easy, and I'm not sure I could even hit 30 on my touring rig (it doesn't have a computer). If I can, it would only be for a few seconds. I can also climb faster on the racing bike.
A 0.5 mph difference on a 20 mile ride will work out to about a minute and a half. 0.5 mph will not change which riders you keep up with and which ones you leave far behind, but it is noticeable. On the other hand, I'm not sure you'd get a 0.5 mph difference between a $1K bike and a $4K bike.