@Netyaroze good post but I think that the next gen will be about 10x more powerful especially as they wont be out until 2011-2012 at the earliest (2010 is possible especially for Nintendo but unlikely) and graphics processor are already almost 10x more powerful just look at the 360s xenos at 240 GFLOPS vs the Radeon HD 5870 and HD 5850s 2720 and 2088 respectively.
by 2012 it will be closer to 15x more powerful and even today's chips would make a noticeable difference for Microsoft especially as they will be able to implement DX11 level effects and framework + deliver 1080p with 4x AA instead of sub 720p with 4x AA
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