That is surprising to me.  I did the trial of C4D and C4D render times were much lower than C5 for me. I finally settled on 3dsmax, for various reasons; one of them being that it is has bit lower render times (but not much) than C4D. But honestly, it is very difficult to get a realistic render time comparison; because every app has different features and settings.

I found VRay to have very efficient GI, not as efficient as FinalRender, but not far behind. It also has many render features that C5 doesn't; and a lot more parameters/shaders/etc.; naturally it has a higher learning curve than C5 as a renderer.
Learning curves are, of course, relative: C5 is a dreadful learning curve for me, the GUI seems very haphazard and disorganized to me; but not unlearnable (it is just taking time). Poser's GUI is beyond me; I gave up a long time ago trying to use it. 3dsmax (which is always said to have a terrible learning curve) was much easier to learn for me; it has very few cryptic icons to decipher and is mostly menu driven, mostly numeric inputs. More compatible with my brain patterns, I suppose.

Overall, the more features you activate, the longer the render takes. It is impossible to multiple # of calculations without multiplying render time by a like amount. So a more advanced renderer might be said to be 'slower'; but in reality, it could be much faster (i.e. more efficient) and is just doing many more total calculations; with an end result that a less advanced renderer cannot duplicate.

Friends don't let friends use booleans.