Nilz--you are in 10.9.0 I take it? Is OpenCL working on the Titan? It is not in 10.8.5 for me. Please test with LuxMark: http://www.luxrender.net/wiki/LuxMark
Cinebench (OpenGL) performs much better on Windows. This has nothing to do with power management and is not a "problem." As I understand it, OS X never runs the most current implementation of OpenGL. If you want OpenGL (gaming) performance, then you should be using Windows.
Your CPU not changing ratios properly might be fixed with native support for IVB-E, but if you are alluding to overclocking via multiplier, then I am not aware of any solution. You should not install NCPUPM.
I switched to BCLK overclocking instead.