You may not really need as many fasteners as you may think when you can get lag bolts into a stud.
I have a 55" Samsung LED TV mounted on an extending arm mount and it doubles up on lag bolts, so 4 of them vertically.
With a 65" screen and studs that should be 16" on center, you should be able to get 4 lag bolts in, two in each of two studs. Even if it's off-center from the TV screen that's covered by the TV and still holding onto it just fine.