Stock 17/39 is good for just highway stuff. Depending on what all of your riding consists of, you could even consider going a tooth larger on the front or a tooth smaller on the rear as well. 18/39 or 17/37 or something similar. Never done it personally, but those sprocket sizes should be available. And you definitely want to be wearing ear plugs while riding. Helps a lot drowing out the bad noises, but you can still hear plenty good.
08 ZX6R Radial M/C ZG Sport Touring Windscreen CBR600RR Calipers BMC Street Filter
GP Shift Pattern DIY Mod Fender Eliminator Kit 16/44 Gearing Euro Flushmount Signals
Gauge Cluster Color DIY ModSoupy's Fully Adjustable Lowering Links HEL Stainless Steel Braided Brake Lines