The other point to this argument is that if you could have no lag, you would, wouldn't you? I would. Riding the wave of power created by a turbo isn't the only way to having a quick car.
Personally I'd be looking for a system where the power doesn't come on so violently, meaning a smoother torque graph and better driveability throughout the whole rev range. This isn't possible on a bigger turbo because of the way boost is created, so a compromise is required.
I went for the small turbo option for the above reason, although IMO even the PHR stage 1 kit comes on a bit too strongly for what I want. Power is OK, but maybe big twins would provide the setup I'm really after.