Yes, most people are running 17" rims. This is the popular size that you can find some really good tires in. I have 110/70x17 front and 130/70x17 rear. The wheels I will be selling soon are 17" excel rims in black, with the KLX hubs.

 

With the slightly smaller rear wheel I guess it would have a slower top speed? Is this correct?

 

Yes, it would lower your top speed a little, but I can get you a sprocket for them, 39T, which will bring your top speed back up. They come stock with 14T front and 39T rear here, and I can easily run down the road at 110kph, all day long.