Like most things (not all), I suspect that disaster doesn't loom just over the horizon at 66mph. With that said, I do believe that every mph increase does marginally increase risk, as does various road conditions etc. Following this logic, I'd risk less tire issues running at 40mph - I believe this to be true but the marginal risk improvement isn't worth it. I'm sure that the marginal risk increase from 60-65 is less than the risk from 65-70, or 70-75.
With all of that said. I've chosen to pull at 65, and havent' had any tire issues in many thousand miles of travel. The risk of tire problems at a faster speed may be small, but it's smaller at 65 and I've been fortunate.
Frankly, there's a side benefit that is much larger. Since I'm in the habit of setting the cruise at 64/65mph and sitting in the right lane, I've found that there is very little stress and the driving is easy while I watch the scenery. I actually prefer pulling for that reason, if I'm not pulling I'm fighting traffic more and worried about getting pulled over for speeding etc.
YMMV
