It all depends on the setup with the intercooler, exhaust, etc. You can get a T3/T4 to a point where lag is almost non-existent. I have the tiny greddy turbo on my car and it is fully spooled by 3000rpms, so I don't really have lag to deal with. The only issue is the size of the turbo restricts higher power outputs. You have to give something up to get something: you either get lag but tons of power once the turbo is spooled, or you get a smaller turbo that spools almost instantaneously with very limited power output. That is just the reality of turbocharging any engine.