The furthest I have gone on one of my freakbikes was ~30 miles (lot of hills) on an 8'2" long chopper. Tallbike usually stays within a few miles of home, I use one of my fixies, cruisers or road bikes for most rides more than 10 miles. I am thinking of doing a ~300 mile round trip on my tallbike from Duluth, MN to Minneapolis this spring.
People have been riding all kinds of wacky stuff for 200 years. It's really hard to say that this or that was the "longest". I mean, Skunk's odometer has 13,000 verifyable miles on his chopper, but that's over 12 years. People who simply only ride a chopper can easily reach those numbers by commuting for a decade.
So I commuted on a triple-high for about a year, I was riding every day but I never left town, does that mean I have a "documented ride on a tallbike" for 1000 miles on a triple?
The reality is that a well-built freakbike is often easier and more enjoyable to ride than a shortbike. When you're touring your bike weighs 200 lbs no matter what, and if you have one that's custom-built to your dimensions AND a joy to ride, it's really no great feat, it's easy, you can do it!
Thomas Stevens rode his pennyfarthing across the united states in 1884. He wrote a book about it, "Around the World on a Bicycle by Thomas Stevens", which is the original bicycle touring book. Have you ever ridden a pennyfarthing? Aside from the fact that it's a tallbike, it's also a fixie, has a teeny wheelbase, traps you under the handlebars when you take a header, can't handle big bumps, and has no brakes. He rode it across the U.S. at a time when there were no paved roads and no highways, just cobblestones or rutty dirt country roads. Then he rode around the world. I really don't think anyone's topped him since.