Not sure of the vtec crossover on your ecu now, but do note that the difference between 4500 and your current crossover will not be getting the fuel to match the air you let in with the big lobes.
Hard to say how lean you'll be, but it is something to consider. Could be a nasty spike.
Also keep in mind you can hit vtec while the car is sitting still, taking off (maybe in too high a gear, causing a load bog + lean = boom). Just be careful how you drive it.