When I looked into the SCT, the best option was the Pro Racer's package. It's the same thing a dealer would use to write you a tune, but only for one vehicle. Unlimited tuning and then you write it to the handheld. You are going to need some dyno time to make it work. SCT does offer a tuning class in person in sunny Florida or now I think they do it online as well. Megasquirt is a great option, I have my W350 running on a salvaged Holley ProJection TBI system. For the most part it runs pretty well. Some of the finer things take quite awhile to get it to run factory smooth. So be aware you may be spending copious amounts of time tuning. I think MPI would definitely be easier, and some day I might convert over to a Magnum top end. I think one caveat of using the MS on a newer vehicle is you have to share the sensors unless you plan on ditching all the other computer controlled systems. The factory PCM controls more than just the engine; it controls ABS, airbags, transmission, gauges etc. You ditch that, you lose everything. So what they do is piggyback the MS and trick the factory PCM that all is well so it doesn't throw a million codes.

As far as turbos and PSI, we need to know your HP goal. You can get fairly insane without much turbocharger. The T72 will still be viable up to 1000hp at 23psi. Only with a smaller compressor would you need to run a higher boost pressure, to make up for inefficiency. 650hp at 11psi sounds pretty fun to me!