As a result, Edge reports that the game runs at "just 20-30fps" on Sony's console. Carmack places the blame on the PS3's GPU -- the RSX -- saying that, "The rasterizer is just a little bit slower -- no two ways about that...the RSX is slower than what we have in the 360." He sees both consoles as being comparable in terms of raw processing power, however. "The CPU is about the same, but the 360 makes it easier to split things off," he told the magazine. "...that's what a lot of the work has been, splitting it all into jobs on the PS3."
Now, before you go making a comment you can't take back, know that the Edge article doesn't clarify whether or not the performance of the PS3 version will be improved prior to release. It's also telling that Carmack states that the PS3 is only "a little bit slower" than 360 in his findings -- if that's the case, we can't imagine that the finished will run at fully half the speed.
Update: Further comments from the Edge piece reveal that the developer is indeed aiming for parity between all platforms. "Everything is designed as a 60 hertz game. We expect this to be 60 hertz on every supported platform."