Not trying to argue on this as I know the es is a great pipe. But every es pipe I have heard is louder than my setup. Especially on uplines. And I believe the greves puts out more power from what I have read.
Also check out the aeroslave pipe. A little louder, lighter, and more power.

And I can't find anyone who sells the os greves pipe that piedmont carried. Now you have to buy the webra greves pipe.
Same pipe I have on my OS now..