Re: 6.5 Grendel velocity
22 to 24" barrel from Satern, +2 gas system, "small" gas port, 8 or 8.5 twist and you'll be able to run pretty much any bullet you desire.
If you are not going with extended gas system, stick to a 20" barrel IMHO.
Single loading the 130s would be hard to beat.
Out of magazine the 120s are best bet for beating wind.
AA / Laupa brass would be my first choice. Buddy has used some Hornady but case mouth required extra attention as it had pretty large burr. If your time is worth anything, AA/Laupa is the safer and cheaper option long term.
Longer barrel will pick you up a bit in velocity but not enough to stabilize a bullet. 9 twist will probably work with all but the heaviest of 6.5mm bullets but an 8 twist won't hurt you any either. See Satern has some 8.75 twist barrels in stock. 120 and under, 9 twist will do just fine. Plan on running anything larger, I'd go 8.5 minimum and prefer an 8 twist.
Problem with the bigger, longer bullets is you lose a fair bit of case capacity when running OTM, if single loading than not as big a deal. 120 Sierra and 120 Berger Match BT are nice OTM bullets. 130 JLK is great single load bullet but you'll be about 2.475" OAL.