I've had a stage 2 Jetchip installed for several months now. Does it make a difference? Immediately. But I also have an intake/TBS, cat-back (no headers tho, I think it runs better with oem manifold) and the Firewire ignition. Combine it all together and it makes a very big difference.
One thing... With all this it did tend to run hotter. I've put in a 160 degree Robert Shaw thermostat and an electric fan (and I carry my old mechanical fan in the parts box in back just in case). For normal driving I can use 89 octane, but add some 91, whoohoo