CoD 4 runs at 1024x600 on consoles.

So, being that these graphics cards are running the game at over twice the resolution but at under half the frame rate, and there was (most likely) significantly more effort to optimize for the Console version, it would be fair to say that the HD console's GPUs are (roughly) in the same range as the ultra low end of the R700's performance.

Now ... I think we got sidetracked on the original discussion.

I think that it is highly likely Nintendo would take a higher-end version of this GPU, modify the hardware (most likely) to improve effiency and real world performance, move it from a 55nm manufacturing process to a 28nm (or smaller) process to reduce size, energy consumption and cost, and pair it up with "better" memory.

Most people don't realize that most processors (CPUs and GPUs) perform far below their theoritical limits primarily due to bottlenecks. Some of the more common bottlenecks are too little cache, too small of a bus, or memory that is too slow; and often these are not "fixed" when a processor is released because they technology doesn't exist or is too expensive to use comercially. When you're dealing with older hardware as a base, you can drastically reduce the bottleneck to get performance closer to its theoritical limits

It is more likely they'll use the RV740 as a base which was already compatible with DDR3/GDDR5 and produced on the 40nm node if they're using that series of GPUs than taking RV770 as a basis given the fact that IGN keep pointing to the HD 4850 when the HD 4770 offered extremely similar performance but is less well known.

By the way the memory sub system consumes a lot of memory, theres a ~8W TDP difference between GDDR5 and DDR3 versions of the same laptop chips FYI so you have to keep that in mind too.

You also have to remember that the PC version was running with a lot more RAM and a faster CPU so it is hard to isolate the the GPU from two different systems.

While I hope they do I think they are more likely to use a small mid range part as their base so they can passively cool the console. Fans can be noisy add bulk and are more likely to break and nintendo like compact silent consoles. 

RAM is probably the biggest bottleneck on current consoles and if Nintendo use a GPU that is 2.5* as powerful as the 360s and add at least 512MB of GDDR5 for the GPU in addition to system 512MB of system RAM they could have games that look run smother at 1080p than they run at 720p on the 360 with better AA and some extra shader effects.