It's a little bigger compressor wheel, so should flow a little more air at lower IAT in a peak potential setup.

 

It's not really BS, it's just a misunderstanding of what "they" say. STS runs smaller turbos because of the spool, true, but the turbos are not "too small". Most people run turbos that are sized "too big" to have good spool times. The reason they run smaller turbos has nothing to do with the rear design at all. In fact, their turbo house recommended the exact same turbo for my front mount as the rear mount... They just size turbos for rapid spool and moderate boost instead of monster boost at high rpms and long spool times.

With A GT70 (T04S backside and a 70mm compressor), I made roughly 600hp to all 4 wheels on a mustang during a run aborted due to setting the plug wires on fire (lifted at 5300rpm). That was with the 408 at at 14psi. The turbo was done there, and I wanted more boost so I switched, but you can see that the "too small" turbo was actually fine and made pretty damn good power. It also reached "full boost" at 3000rpm and started spooling at 1800rpm.

Having said all that, STS routinely recommended turbos to me that were too small to achieve my stated power goals. Yeah, they could make great power, but would have been at a horrible efficiency range to make the power I wanted. They always spooled very quickly though

The mp70 is likely pretty close to done in at 13psi -- you could probably tweak a bit and get it a tiny bit higher, but it would be inefficient boost anyway...

 

so the general concensus is that the MP T-70 will be pretty much all done on my new setup at 14-15psi....

if thats the case, the bennie for me would really be just to step up for lower IATs, I dont plan on going over 15psi anyway, and even that would be rare I believe... I'll probably run around on the street at 10, hell, even the wore out 5.3/70 was making enough power at 6psi that driving around town was frustrating... I can only imagine what a fresh forged motor, more cubes, more boost, and bigger turbo is going to be like

hopefully my move to go to a smaller converter is a wise one.... i surely loved the flash on my 3600 under boost, but I believe it was just too much... this thing made crazy tq at low RPM, and I never really used it...

 

what about a innovative gt-72 with a .96 backhousing on a 6.0?