Yeah, the 4G63 is really responsive to modifications and IMO one of the best designed 4-cylinder turbos...Part of its secret, I think, is how the turbo is mounted right off the manifold, close to the source (heat retention)...
The only thing that is misleading about the 0-60 time (stock) is that does not indicate very well its "all around" performance. For instance, if you're in the wrong gear/speed, it can feel like a dog...But, in 1991, it had very good performance (I remember that time well in cars)