Here is the different between a VT3-725 and a VT2-625 supercharger setup, both on DCT M3's with meth in SAE correction:
645 wheel for the built motor setup and 586 wheel for the stock internal setup. VT2-650 kits claim to be over 600 wheel on stock internals so one has to ask themselves if it is worth the cost to build a motor for only 50 wheel horsepower? $15,000+ on top of the supercharger kit for 50 wheel? Sure this power will likely be more reliable but one has to scratch their head at this price for performance ratio. It certainly makes sense to upgrade to a VT3 setup if one were to take the stock motor too far though.
The Vortech blower used here is approaching its limit. For a built motor application, it would seem to be a bit undersized as 12 psi is not providing all that much versus the 7.5 psi of the stock internal kit partially due to the lower compression. To really see solid gains a bigger blower is necessary. Gintani has shown up to 16.5 psi with a Vortech YSI thus far and higher dyno results on the lower reading Dyno Dynamics dyno.
Hopefully a comparison of the three major built motor setups will be able to be made soon.