80gr with a .4bc at 2700 rings 200ft/lbs at 1,000 yds, over 300ft/lbs at 700yds which beats a 22mag at point blank.
Now if you're looking to reach 700+ odds are you're running a bigger rig, so you're probably pushing the bullet a bit quicker and depending upon the 77, 80, or 90gr bullet you may be over .4bc and I believe the 90gr Berger is .551. Meaning those numbers above are low at best.
If you are running a 16" rem sps tactical, well, odds are you aren't looking to or capable of anywhere near consistent sub moa precision at 600+, so you're limiting yourself.
So, 223 running the .551bc 90gr Berger out of your 26" custom rig that allows you consistent half moa, 1,000yds, 800 would be plenty safe.