Usually I find that you get less traction going too low pressure wise on tires with the 690. I think it's because the heavier weight of the bike over say a 500 is causing the tire to flex sideways on the rim. I tried running my tires down around 14 thru rock gardens (on my 525) having been told that over that pressure gave no benefit. I **** two rims over the course of a week!
I don't think a real street legal knobbie is gonna give much mileage or confidence on the tar full stop. There not made for it.