Sigh ... It really doesn't matter which system is more powerful
We have hit a point of diminishing returns in the impact of increased processing power has on the appearance of a game, and we have hit a point where it is probably a bad idea (from a business perspective) to push either console to its limits due to development cost vs. potential sales. I'm not saying that no games will push the hardware, but companies like THQ and Activision will probably produce most of their games with little consideration for the theoritical processing power of either of these systems.
The best looking PS3 games will look roughly equal to the best looking XBox 360 games ...







