The 175 grain bullet is the "go to" bullet for long range, because it is heavier and thus has more momentum. The 168 grain should be good out to about 700 yards or so. The key here is velocity. Why?
Picture the lonely bullet, coming out of the barrel at around 2600 fps. It's cooking right along--and right behind it is the turbulence caused by the bullet's passing through the sound barrier.
When the bullet hits the sound barrier in velocity (roughly 1100 fps) the pressure wave catches up to it and kicks it mightily right in the rump. The bullet quickly loses stability and becomes inaccurate past that point.
Now, the 175 grain bullet doesn't have that problem--if fired at 2600 fps, it will stay supersonic at 1000 yards. The key here is speed, and you're going to lose a bit of it with the shorter barrel.
Other considerations are care in preparing the rounds if you handload-sorting, trimming, weighing the cases, deburring flash holes; neck turning and/or inside neck reaming; carefully weighing and separating bullets of similar weight; trimming and evening meplats--then carefully hand weighing each powder charge.
There is also a consideration about WHERE and WHEN you shoot. Colder air, and air nearer to sea level is more dense; hence, you'll hit that transsonic barrier sooner. Higher elevations and warmer temperatures have thinner air density, and correspondingly longer ranges.
You can determine all this by shooting your rifle well, concentrating on following your shot plan and keeping careful DOPE (Data On Previous Engagements) recorded, in as many different conditions as possible.
Hiding in plain sight...