Road 6s are indeed great tires, but Michelin is mighty proud of then price wise. Another good premuimish tire to consider is the Continental Trail Attack 3. They lasted for my entire 20 state 30 day big west tour with tread to spare. Even at 9000mi the handling was excellent.
That said, I tend to be a tire slut and buy on price. Any of the top brands (Michelin, Metezeler, Dunlop, Bridgestone, Continental) are going to be fine, I can scratch the GS pegs with any of them. For reference, I've ridden and can recommend the following for an adventure bike:
- Dunlop Trailsmart, I went through 6 sets of these when one of the online places was blowing out excess stock at $120 per SET!!! Great handling wet and dry, not super long lasting
- Bridgestone A41 - Great wet/dry, longer lasting than most, good pricing. Cast iron b!tch to mount, though. If these were easier to mount, they'd be my go-to
- Metzeler Tourance Next - good all around, on the expensive side
- Michelin Anakee III - Great wet/dry, not one of the longer lasting tires, but buy them when I can find sets for well under $300
- Michelin PR6 - Everyone knows how good these are, probably the most expensive, and they don't outlast the A41 or TA3
- Continental TA3 - Probably the best overall tire I've run on the GS, fantastic handling and feel, and good tread life. On the pricey side, but will be my go-to when I can't find the others at a screaming deal price.