How much difference it would make depends on the modifications you have done to your engine. Since the VTEC system exists to provide the utility of two different cam profiles (one for low rpm performance and one for high rpm performance), I think it is safe to assume the Honda engineers set the activation point at the place where the torque curves on the two profiles overlap (or close to it) and the second cam profile becomes more efficient. If so, it only really makes sense to lower the activation point if you have done something to make the second cam profile more efficient at a lower engine speed. Forced induction that comes on fairly quickly would be an example of this (Bell TT kit, for example). If you have not modified your engine in a way that makes the second cam profile more efficient, I would not think it would make a noticeable difference and, if you were to lower it significantly, it could actually decrease the performance of the engine.