Chael Sonnen is a good candidate for showing off it's efficiency.
Chael, IIRC, is the only MMA fighter to date to get caught with actual EPO, and he's also a fighter known to push through 5 rounds with the same grinding pace throughout. People used to call him an LnP artist, but in truth, his activity level whenever in top position was extremely high, and he definitely didn't conserve energy in his takedown attempts either.
And let's face it, if Chael wasn't already on top, he was most likely pressuring you non-stop and looking for that double.
How much of that cardio and muscle endurance is attributed to EPO is a tough one to answer though, but having extra blood cells to carry more oxygen to your muscles certainly can't hurt a wrestling based fighter like him.