How much does singlespeed slow you down?

Yeah I know about the Athletes hour e.t.c I', not a complete idiot but not everyone does that do they. I mean a stage on one of the tours, mass start mass finish public roads decent length e.t.c
edit @hippy

With everyone on the same bike? Why? They have enough bikes. They'd get nothing from bike sponsors. They're all on different drugs anyway.

Here's something more your style Captain Retrogrouch:
http://www.sportstoursinternational.co.uk/cycling/leroica