I honestly don't know how that bullet will perform in that barrel at those velocities. The one guy who ever got good results at 1K with 168gr BTHP's in a 308 Win was using a 1:13 twist in his barrel, which goes against the common wisdom about twist rates and transonic bullet transitions.
With a 1:10 you are looking at 11% slower rpms on the bullet than the standard 1:9 twist that everyone says is good to go for up to 130gr bullets. 8% lower mass, 11% lower rpm, your initial velocity is going to be pretty high from the 260 Rem case, I think you are in no danger of going subsonic out to 600.
I'd say go for it, as if the 120s don't work out there are some good choices in the 90 to 115gr range that you could fall back on that are sure to be stabilized with a 1:10 twist.
Sorry I couldn't be more help.
Machine guns are awesome until you have to carry one.