Your issues seem to be specific to your system (I and others have reported 3-4 core usage above) and if you're seeing 50-60fps, it does rather beg the question why you are complaining.
Few LCD monitors can generate images at more than 60fps so you're likely near one hardware limit and if your graphics card is too hot, then that's more a cooling issue (my 580GTX reaches 70 deg C). Get a bigger fan!
There is a difference between "complaining" and talking about tech. My graphics card is pretty well cooled but many people reported that the game really seems to stress the GPU on a constant level (more than 80-90% load all the time). I personally don't think that the graphical fidelity of the game is good enough to justify such an intense load of modern GPUs. I mean the game is pretty but that's more a question of art design and not so much of technical features imo. I mean the game stresses my GPU and my CPU (and obviously not only mine) more than let's say Assassin's Creed Black Flag which is quite impressive on high-ultra settings. There is no obvious reason why the game uses 90% of both CPU and GPU in some sceneries, that's all. I can only imagine how the game runs on less powerful PCs...
My only real personal complaint is that there are some framedrops from time to time and stuttering while scrolling the map.
And I have a pretty "common" CPU, a Xeon E3-1230v3 which has become quite popular lately. It's basically an i7 without the possiblity to overclock it. The tech is the same. So I doubt it's me alone having the game only running on one or two cores. If at all the game is not optimized for my hardware, that might be the case. But that would give me quite some reason to "complain"...
