Somehow I don't think the theoretical performance of either console will be a deciding factor. How the game developers use it will be much more important, since both systems are unique and proprietary. However, if I were sony, I would be concerned about the length of time between the consoles. The 360 has a year head start, and that means a number of things.
#1. A die shrink which will make the 360 cooler and cheaper
#2. More games will be available when the PS3 comes out
#3. Games will take better advantage of the hardware, as dev's will have been working with it for over a year
#4. It's been out longer, and many customers on the fence will have bought the available 360 instead of the "sometime late 2006" PS3
#5. The one year time the 360 will have been out probably means Halo3 will be ready to be released alongside the PS3. MS probably would have released halo 3 even if the thing came out 5 months earlier, but with the ps3 coming out in november, I doubt the game will be nearly as rushed.