They work great on the engines they were intended for, but the TIV isn't one of those.
Look at that picture and you'll see that the number 2 cylinder is directly under the cooling fan, in this arrangement it gets hardly any cooling air. The same can be said for #4 and some systems make it even worse as the tangential flow of air being produced by the fan is directed clockwise, more toward the 1-2 bank. This puts #4 opposite the tangential flow as well as almost directly under the fan's discharge.
Thats not the case with cylinders 1-3 as they receive a ton of air and actually overcool. The bad part about this is the fact that the same cylinder head can have one of its cylinders overcool and the other run hotter thus increasing the differential of temperatures on the same head. This leads to heads that lose torque values and heads that can warp and not seal well.
Here is a run to the top of Loveland Pas at the Continental Divide on my R&D trip from 2006. This is a run from 5,000' up to 12,000 feet with a 180 HP MassIVe 2270cc engine being held at WOT as much as possible.
Note the temperature differentials between all 4 cylinders at full load and WOT.

The 911 system has looks, but thats all it has. If you want that look, just install the engine into the car that had it from the factory.
My X4CS Carrera style cooling system will be V 3.0 of the DTM, using the DTM characteristics with a completely different look using a dual inlet fan and many attributes of the Carrera 547 4 cam engines. Release will be mid 2009