All VTEC does is make your engine (more) efficient at higher RPMs. Basically giving the engine a new lease on life around 5k when most other non variable timing enabled engines seem to lose their guts. Its not a magical silver bullet and ALOT of car makers use similar engine management to VTEC. Ferrari for example has a extremely efficient version which basically uses 3d cams so instead of a on/off switch like VTEC the car is always making as much power as it can at any given time. Very nice. iVTEC is similar in power curve I think but I have not done my homework on it because I don't have a car with it nor am I getting one. =)

A turbo car will be able to make more power than a GSR easily and it would probably be faster in all cases. The only downside that I could see besides running boost in a engine not designed to be turbo'd is that you lose out on the normally aspirated feel to the car and the sound and whatnot. Some people just like NA cars more than turbo'd cars. I like NA more than I like a turbo'd car but I'm not crazy about spending a hellva lot of money trying to make a NA car faster...I don't own a domestic or anything so the gains don't out weigh turboing of course...anyway now im rambling and im going home