The compressor wheel on that 6665 is ancient technology, a giant cast chonk of a wheel.
A billet compressor 6262 will outflow and outspool that by far.
With that being said, I'd go with the larger t4 back housing, especially on a 4.1L motor. you're going to be taxing that 62mm turbine unless your heads flow like dogshit.
There are ways to mitigate lag in tuning and other things, but high backpressure is a bitch, and makes tuning a LOT more difficult with exhaust reversion.
What are your cam specs? Lift/duration/LSA?
90 TSi AWD Auto - 10.359@128.41
Best MPH: 132.21
Best 60' 1.490
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