I have heard that there is some math involved after changing to a 22" tire for your gearing. I'm not sure about the specifics but to get back to a stock feel after going 2"s taller in the rear you would need to go one tooth smaller on the front and add one tooth to the rear.

One thing to keep in mind, every 1 tooth to the front is the same as 3 teeth in the rear.

on our z400 we went one smaller on the front which shortened our overall top end speed but gave it considerable more bottom end.

a 13/40 will give you a little higher top end then stock if you were still running the 22" tires. but since you are running a smaller tire you should see an improvement in your bottom end. (me thinking aloud) 

I think a 13/40 set up should be a pretty decent all around set up. let us know on what you think once you get everything set up.