You could also switch out the front 15T sprocket for a 17T. That should make a noticeable difference at highway speeds. Look for the post by MattC. He just upgraded his to a 16T and likes it, but he's going to change that one with a 17T sometime in the future. It's a quick, cheap fix.
The VL800 is shaft drive...no sprockets to change.
The reach for a non-existant sixth gear is just one of the drawbacks of a small displacement cruiser. In order to get good performance at low and mid range speeds, the gearing makes the RPM at highway speeds rather 'busy'. I prefer the power around town and up in the mountains, so I love my 800. But for highway trips or sustained high speed operation, the best bet is a bigger bike (I have a Yamaha Voyager for long trips on the interstate). There is no way to swap the gear set of the drive unit, as niether Suzuki nor the aftermarket make different gears. But the design is far more complicated than the rear end of a car, so you can't swap out gears like you can on a car. Nor does anyone make a primary drive gear or a different gear set for the transmission.
I was the one on the other board that modified the VS800: a taller rear tire and a shaft drive unit off a European spec VX800 gave me a 10% drop in RPM in fifth gear. Because the VS800 motor really makes its best power above 4000 RPM the bike's performance suffered at lower speeds, but it did make the bike more confortable at 70 MPH on the interstate.
I don't know if the VX drive unit would fit on a VL. They are also pretty hard to find, as the VX800 was only manufactured for a short time, and went out of production on 1992. The drive unit was also an inferior design to the VS and VL units, wearing out fairly quickly. By comparison, the original drive unit off my 1996 VS800 has 130,000 miles on it and shows less wear than a VX800 unit with 18,000 miles on it. I put the VX800 drive unit on my other VS800 and ran it for about 3 months, but once the unit got to 25,000 miles it was shot and I had to swap it back. All in all, it was not worth the effort.