Go down one in front, keep the old sprocket. If you don't like going -1T front, change the other back IF it's still good/straight/not too much wear.
I am -1T front, +1T back. I LOVE it. Super fast acceleration over stock plus my aluminum rear sprocket weighs a ton (okay around 4 lbs) less than the stock iron rear sprocket.
Be aware, if you do a lot of highway riding, it may irritate you -- it does for me when I do a lotta highway cruising between cities when I have to. It's like not having a 6th gear (RPMs high) Doh.
But yeah, more than a pipe, rejet, ignition advance etc, going down one in the front will make your acceleration stomp ass (vs stock). It's cheap too
'00 ZX6R silver