The Evo engine's internals are generally so light, it's like trying to trot on a quarter horse that wants to gallop away. It feels best either accelerating or decelerating through the canyons and I love it!
I have kept stock high gearing with 6th as an over drive that loads it up on the highway to counteract this tendency so it only does 3500 rpm at 60 mph. The bike has also been carefully tuned to smooth things out at cruise. Remember that the factory lightened the Evo's primary gears, timing gears, crank, alternator and flywheel like a race motor. Some of my buddies on sports tourers hate it, but they're pussies.
I think the 620 has pretty light internals as is, so the effect would not be as dramatic as on a 900 or 1000DS.
funny you said that, i finally fixed the monster and after not ridden it for over a year, i took her out for a spin, and had the same thoughts. its a good and bad thing though. when your having fun with it its like an instant on off button, but it makes it real annoying in the city!