this was the first mod i did to my bike. i have a 15/42 setup right now and i love it. yes, it does reduce the "zippiness" a bit, but i ride on the highway alot and the setup i have reduces rpms and makes it more bearable.
+100 for the gearingcommander site, itll tell you everything you need to know about every combo.
this also helped me in picking a combo