Most games made by intermediate game developers will have the programming matter more than the language used. The C++ AAA games are created by a team, typically, which can utilize the full features of that language. It often takes years to make an AAA game, let alone learn the language added to that.
Most games don't even need the extra features of C++ advanced programming in the bigger picture of things. Most of the games no matter what language if programmed well will not come close to the performance limit of the hardware and should not in any case.
If you really want to learn C++, then do it, but we let you know what you are facing.
As for the link to the benchmark of C++ and C#, many things are not mentioned here, such as optimizations, NGen beyond that example, compressions, filters, buffers, wrappers, frameworks, and
just pure need: (Edit: Fixed!)
http://code4k.blogspot.de/2011/03/benchmarking-cnet-direct3d-11-apis-vs.html#!/2011/03/benchmarking-cnet-direct3d-11-apis-vs.html
It does not include the human factor.
Clinton