Original gearing is a bit short. Go to 15/43, and you'll be happier on the highway. With this gearing, you'll be in 6th at about 45/50 mph. The engine is pretty happy to cruise at 3200 rpm. If you want to accelerate, you'll have to downshift. It doesn't hurt to spin it at 7000 rpm, redline is at 10.5.
Sure, a big engine will enable you to attain higher speeds at lower rpm. But consider what an 1800 cc Gold Wing weighs and what the fuel mileage is. There's a thread here concerning someone who took one of these 650s to AK and back with no problem. It's in other bikes because it was an ER-6, but it uses the same engine. Ride it, enjoy, and keep up with the maintenance schedule.
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