I have a TT T38 on my 3dr. Its got a .76 A/R compressor with a .63 A/R turbine. I had the engine biult and dyno'd by Harvey with which i supplied the turbo. He had trouble making good horse power out of the turbo as the waste gate wasn't up to the job. Sent the turbo off to be modified, then it made 432BHP on the dyno.
Ive had T34s with both 48 & 63 turbine housings, and the T38 compared to the T34s is not worth the extra money. I paid £900 for the turbo, £100 for the waste gate modifications and £700 to have it live mapped. I wish i had thrown my money at a T4.
I would rate the T38 as having the same amount of lag as the T34 with the 63 turbine housing. When the power comes in, it comes in much harder and is still making BHP at 7,000 revs. But you would need some serious head work, cams and lowered compression ratio to run this turbo.
If you wanted it to be responsive with good power, 380BHP, i'd go with a T34 with a 48 turbine housing, which you can get a cheap off the shelf eprom for. If you wanted big power go down the T4, GT30 or GT35 route.
The T38 is the one in the middle of these.
It drives nice around town and holds good power all the way through to 7,000 revs.
The power graphs are old but you can still make out the power run.
Regards Paul