I asked a friend of mine to test it out, see if it was just me or my machine. Below are some emails I received:

Email1:
Well I manage to get 16.7% CPU which may mean its using a core and a bit or turbo boost is making the numbers weird and 6% - 20% GPU.

And even dragging the window round the screen seems jumpy. Does not seem good at all.
That's was vs2010. I have found that mingw does worse than visual studio in terms of perfomance and threads also don't seem to work correctly with mingw.

The specs for the computer are:
i7 2600k @ 4.85ghz
NVIDIA 570 gtx
Windows 8 pro 64 bit
Qt 5 64 bit dynamic


Email2:
I just built it at work using the qt5 from the commercial installer and it uses no CPU at all.

The only difference i can think of is that the installed version uses ANGLE.

Email3:
Just tried with vs2012 and its the same as 2010