I'm looking for better response from my T4 and wondered whether anyone had ever gone down the roller bearing route.

I only track my car so generally can keep the revs up above 4000 rpm where the boost comes on but it is the transition from off throttle to on throttle even above this threshold where the lag is really noticable. Even a couple of hundred rpm ealier response would make such a big difference. Just don't want to waste money doing it when there is no real benefit. The turbo is newly rebuilt (2000 miles), ported and with a bigger wastegate penny.