I have an independt fabrication bike. I REALLY like it...if I'd have it since 2007 and ridden many thousands of miles on it.
Prior to that I had a heavier Lemonde (a low end)...didn't have as good as parts...
And the difference in speed, for me, is: marginal....it is better, but just barely...it's more comfortable a lot...
What would make ME faster would be to lose 25 pounds.