I did run my CF650 with 13t in the front, top speed was about 175km/h what was enough in here Vietnam, I did love it in the city as the acceleration was so much better but then on the big road RPM were little high so did not get so good fuel economy you could go for -1/+1 setup. you can check this webpage ->
http://www.gearingcommander.com/
just choose the bike from the list as Kawasaki er6 2009 or so, it will tell you max speeds and much more
ou yeah! I did run my bike with pod filters, you get great intake sounds, but I think it did cost me some torque. It just did not act the way I wanted so in the end I went back to the original airbox.
so in my opinion with cones there are two benefits, sound and the space what you get when you remove the airbox.