Lighter wheels will make a much bigger difference than a lighter frame as far as speed is concerned. This is because wheels are "rotating weight," meaning you propel their weight with every pedal stroke. The frame is "static" weight, and that affects its performance, speed-wise, very very little. The Kona frame may be a bit overbuilt for pure road riding (although maybe ideal given your overall riding conditions), but put a set of lightweight clinchers on there for your centuries or pure road efforts, and you will still have a great road ride, I'd guess, and you should really feel the difference a set of light wheels can offer.