He's said it a couple of times. He mentioned it here in 2006: http://www.gamepro.com/article/news/50983/ps3-more-powerful-than-xbox-360-says-john-carmack/
And he said it again more recently this year. (I'd look it up, but I just can't be bothered.) 360 is easier to work with (so he prefers it), but the PS3 is more powerful if you have the time and money to put the effort in.
And as for those figures: as I said, I have no idea what they mean. Odds are, unless you're a video game designer, you don't fully know what they mean either. Numbers on their own are meaningless, as there may be (and usually are) other factors at play.
As I said, who am I going to believe? A near god-like and unbiased videogame programmer, or a couple of random, biased guys posting on the internets, boasting about numbers they don't fully understand?
