Given that up to 10 mph over the posted speed limit is acceptable, do you include that as part of your push for 70 mph postings? Are you only concerned about tickets traveling a little over the limit? For me, I don't have to worry about cops on road trips now because I'm fine doing 8 or 9 mph over the speed limit. I don't want to go faster.
The segments of interstate / freeway I've mentioned have design speeds of 70 mph. Additionally, factoring +10 mph, it's not uncommon to already see people drive around 80 mph on the 65 mph segments I've mentioned, and nearby 70 mph interstates see roughly the same thing, around 80 mph. On I-85 approaching the I-85 / I-40 overlap, the speed limit drops from 70 mph to 65 mph but nobody actually reduces their speed. They just go 15 mph over instead of 10 mph over, keeping with the flow or greater. Having driven on both 65 mph and 70 mph segments in the Triad in fact, quite recently in fact, I don't think increasing the speed limit would make much of an impact, it would simply bring the speed limit closer to reality (75 - 80 mph) and lower the differential between those following the speed limit and those driving reasonable speeds.
There's segments of 65 mph interstates in the Triad I would -not- recommend for 70 mph, given geometry and design overall that keep people generally at or under 75 mph.
After driving the new Winston-Salem beltway segment recently, I concur that it could easily be 70 mph. No sharp curative, relatively straight and wide roadway, easy to hit 80 mph. US-421 Salem Pkwy should also be increased from 60 mph to 65 mph (debatable if I'd go to 70 mph) between east of Downtown and I-40 near Greensboro. Driving that recently, most people were already driving around 75 mph, some even faster.