Mass Effect Fable and Gears of War for the PS3 would be successful.

Would GT5 be more succesful then Forza on the Xbox360 ?

I really think that everything is just a matter of marketing. The Userbases are not so different as many may think. If you advertise this Games properly they would be a sucess.

A good game is a good game. And with some advertisment the most exclusives would sell as good as on the other platform.

The only difference between the PS3 and the Xbox360 is that PS3 is big in Japan and the Xbox360 is big in US. I am sure if Mass Effect and Gears would never be released on the Xbox360 but on the PS3 the sales figures would the same.

I certainly cant see a huge difference between the PS3 Userbase and the Xbox360 Userbase.

i think your estimates for both killzone, resistance, and mgs4 are quite high.