Render times can usually be reduced by splitting a sequence render over all of the processors, using either a render manager, or simply running ( in your case four) instances of TG2 on a single CPU each. It can actually have quite a dramatic hit on animation render times. This also applies to some other renders by the way (Mental Ray for instance), and not just TG2. I've seen TG2 render times almost halved, and certainly a third cut from the render time, but it also depends on what's going on in your scene. Some quality improvements and elements in a scene can cause a whole lot of variables.
If you think of TG2's renderer as a super-dooper displacement renderer, that should give you an idea of why renders can take so long compared to Mental Ray as an example.