You'll get lots of different opinions on this subject, i'm not saying mine is correct but it suits me.
I ride a Yamaha TTR250 and average 6000 miles per year.
My mileage is probably 60% - 40% in favour of road use, but all this is done on various makes of road legal knoblies which I never run above 15psi back and front. My journey to one ride meeting point includes a 20 minute motorway stretch, when I ride up to 60mph quite comfortably, and sometimes a bit more.
Recently three mates and myself did a 3 day trail riding trip of at least 400 miles, 2 TTRs, XR250 & XR400, there were several types of road legal knoblies between us, all running 15psi and not a tyre isssue for any of us, we do all use rim locks [security bolts] whatever, and heavy duty tubes.
The choice is yours.
Get out and enjoy
2 Yams