My vote is a screaming no on this one. Buells just aren't highway bikes. I hate the highway part of my commute.
It'd need a 6th gear to be considered. At 75-80mph, there's just too much engine braking and noise. The engine's at 4000rpm, and pushing harder than a cruiser bike should.
I get ~35mpg mixed. If I cut out the highway and take side roads, I get 40mpg because I can go 55mph. Above that, fuel economy plummets.
Awesome bikes, but designed for city/twisties/mix. 90 miles would be fatiguing on one. I'd pick up a touring bike on the side.