Its easy to get into the argument where you are comparing variable situations as defined already in this thread. If you want real facts look at the times that people run in these cars.
I ran 12.5 sec @ 111-112 mph in a GT-R with standard turbos low boost etc, usual bolt ons. If you can find a STi which runs consistent times like that in street trim then you've got the grounding of fact to say yes, STi is a quick car. Either way there is no doubt the both of them are quick street car.
That could be extended to your R33 as well. But as I've already mentioned, don't get a GT-R unless you're prepared to go the long haul with it - parts are expensive and parts often fail especially in the older R32s. If you want a well rounded stock car a STi would be a good performer, but to me it sounds like you're happy with your R33.