I thought the STS type turbos had some real benefits in aftermarket systems. The main one is that the exhaust gas is several hundred degrees cooler so the turbos don't have to be oil jacketed for fluid bearings. Therefore it's more straight forward as a bolt on, even though you might not be able to get quite as much power.
But in a fully plumbed system hot air in the exhaust in front of the turbo expands which creates more pressure on the turbine side so it spools faster. I actually understood that was more the reason for the lag, not the length of pipe.
As far as PSI, who knows- it's more airflow CFM then PSI. 5 PSI on a big housing can flow alot of CFM. And STS's run pretty large turbos. I see the appeal if you are trying to keep your engine as stock as possible.
Most of my turbo knowledge is from my truck though. I haven't messed with my car's turbo so I'm not sure if it 100% applies.