I'm talking street use Mitsu set-ups, not F1 twin turbo set-ups that last only one or two races before replacement is needed.
Your right about the reduced back pressure will help overall flow which does create a more efficient turbo. In case of the 14B though, your going to max it out at around 34lbs/min. Sure you can try go up to 30psi and maybe squeak out a little more flow, but That is if you want to blow a crap load of super heated air into the intercooler. Perhaps if you had an incredibly efficient intercooler it would be good. Then yes you would need a bigger housing to support that additional flow.
But...
A 14b will hit it's choke at around 20psi anyway, so all that goes out the window. Look at all the record breaking 14b cars. They run the stock ported 6cm housing for a reason. It puts the turbo into the sweet spot. Sure if you have a stroker motor the extra flow will help, but then the 14b wont deliver the air needed anyway.
My point is, why spend so much money and effort into pushing a 14b so hard and end up with 300ish whp? You can buy the FP68hta (basically a 20G) for less than 1k and that will flow up to 48lbs/min efficiently. That turbo was designed around the 8cm housing. From what I've heard it can push past that, but then the housing is the weak link.
My 14b with a 7cm housing maxed out at 20spi still only made 280whp. After 6k it was worthless too.