I only tried CE once with a buddy. We took turns turning it on and off and playing with various settings. It does make a difference but not a huge one.
When we were running, whichever of us had CE turned on would "jump" a couple spaces every 8-10, so the other guy would be running beside him, then suddenly he'd be 2 spaces ahead, then 4, then 6... like that. It's not like CE makes you blazing faster then everyone else.
At least we didn't see it when we played with it. Maybe we were using it wrong.