I have an Ultra7 and have discussed it's installation via 9/16x24 threads with TBAC extensively. 0.650" is plenty for that. In fact, I have a barrel that is smaller than that with 5/8x24 threads. It just barely worked, but it did work. With 9/16x24, it's no problemo. I used my GAP .260 with TBAC...
Both of my 300WSM like 66.5gr RE17 under a 168 TTSX for 3100fps (22" bbl). Accuracy is 1/2 to 3/4 MOA. Really nothing that can't be done with that combo.
68-75gr .224 E-Tip with an expansion threshold of 1500fps. Give it a sleek design like the ABLR. Own the Ar15 world.
110-120gr .308 E-Tip with an expansion threshold of 1500fps. Own the supersonic 300 Blackout world.
200-220gr (+/-) .308 E-Tip Subsonic with an expansion threshold of...
That QL info is a bit surprising. I've done a work up all the way to 24.0gr with no pressure signs at all. Great accuracy and velocity out of my 18" AR.
If you're limiting yourself to 250 yards there won't be much difference due to BC. I'd suggest you stretch that limit out to 350 yards, at least. It's easy to do and even 350 is a chip shot with a little practice. Distances in antelope country can stretch quickly.
Big +1 on the 120gr 6.5mm Accubond. Give it a longer boat tail to help with the bc (ala the 123 scenar or AMAX) and you have the perfect bullet for the .260, creedmoore, x47, etc...