Originally Posted by
terrymorse
Well, not exactly no difference. There's a small difference.
The uber-expensive bike will be at the UCI minimum weight limit, while the $4000 bike probably will be about 3 pounds heavier.
For an average-sized rider putting out 200 Watts on an 8% grade, that heavier bike will be slower by about 2%.
As a rough rule of thumb 1 kg costs an average rider about 1 min on a typical 1 hour alpine climb. Not a big deal if riding alone, but might be enough to get dropped in a group.
Bikes in the OPs price range will be acceptably light, so not something to really worry about.