I purchased GT3071r in last November and before I did, I spoke to Garrett and ATP turbo both to consult whether I should get GTX over GT series.
Their answer was, if I am not looking to get over 500whp then it is not worth paying $300~400 extra to get GTX. Also spooling time is very minimal to notice.
with my 3071r .63 I get full boost @ 3500rpm. I don't feel much lag at all.
Just FYI...
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