In my experience, there are arteries, and there are arteries. The ones that are lightly travelled enough during your commute time that the drivers can pass you in the left lane without any difficulty, are no problem (except for ignorant drivers, but that's a different subject). I minimize or avoid riding on arterial roads with more or less continuous traffic in both lanes. Sounds like your major artery is in the latter category, so I'd go with all-paved, safer. By the way, I found that hills tend to make my average cruising speed faster, in the long run, due to the conditioning effect. I'm thinking of significant hills with at least 1/4 mile of steady climb, not so much rolling hills where you're effectively "sprinting" for only a few seconds at a time.