did you see this page? he dynoed just the "stealth" cai and it added 6hp and 7ft/lbs TO THE WHEELS. not bad, and you can feel it, really helps with response times and such.
and fororec, this is possible on yours too, just take off the top half of your airbox, and take out the filter, then get one of those cone filters and stick it on the end of the existing tubing. as i've said above, we did this to a friends zx4 with zetec, and it helped alot as well.