Originally Posted by a_ump
if it were to be an HD 4800 series, it'd be ridiculously powerful. The 360 uses the Xenos, which is like a fusion of X1950/HD2000 series, and look at the visual's we can get. That's roughly a 6 year old chip/architecture, i'd almost say HD 4800 series would be overpowering. I can see a low-end HD 5k/6k gpu being used thou, as even those have 320+ Shaders compared to the current 48 in the 360.
How about something based on the HD5700 series
It is so successful that AMD is still making them as the HD6700 series.