I'd go for the T66. Yes it lags compared to stock ones but it's all about driving skills. If you are skilled enough, the lag won't affect your performances at all (well, not much). I've already had a ride in a big turbo supra (much bigger than the T66) and god, it pulled. Even from a stop, he could take off like a bat out of hell even if he hit full boost at around 5000RPM. Like I said, it's all about skills.
Plus, if the turbo kicks in at high RPMs, well it means that on regular driving on low RPMs, the car will act like stock and not drink much more fuel.
And it depends on what you want. If you want a top end crusher that's gonna pull and pull go for the T66. If you are interested, I even know a company that sell theire own innovative turbos (very good and robust turbos) and they got one witch spools only a hair later than the T66 (like only a couple hundreads more RPM) but gives you 300+ more HP and tons more torque than the T66. And one supra that has this exact turbo even runs in the 9's on the quarter mile so talk about lag... actually, this supra is the fastest street supra in the world at the track. How come? Well, my friend, it's all about driving skills and the owner of the supra explain this on his site.
Lag isn't that much of a problem if you know how to deal with it.
The site is
www.wotm.com