I'm pretty sure that Silva's going undefeated in title fights and finishing all but 3 of his opponents in his UFC career trumps "winning rounds."
I'm not saying that GSP isn't completely dominating everyone he faces. I'm saying that he has been finished twice and Silva has not. Further, GSP has fought opponents from lower weight classes whereas Silva has faced opponents from above his.
And the piano, it sounds like a carnival
And the microphone smells like a beer