We have ips beetles show up in all our stands, especially after a thinning.
The ips beetle "generally" will jump around and kill a few trees here and there whereas the southern pine beetle can and will kill a whole stand without skipping. 6-7 trees on a 40 is normal and most likely just ips especially if the trees are spread out. One 50 acre stand we had after the drought back around 2000-2002 got really bad with ips that by 07 we had to clear it, but that's rare. Your county forester will be glad to look at it with you I'm sure.
Funny story here, back when I was 13-14 my dad had recently cut most of our property and set It back out in pines. He/we didn't know the difference in ips beetle and southern pine beetle. A forester told him to cut all infested trees and cut a buffer around each tree when he saw a tree that had beetles. My dad worked me and my brothers tails off cutting trees for 2-3 years before we learned we were dealing with ips beetle and it wasn't necessary. For years we'd walk through open areas where we had cut 5-6 trees trying to "stop the spread" of pine beetles and laugh our ass off at how hard we worked for nothing!!!