The 200 in 25/06 has a 1in10 twist. My experience with all 25 cal. with a 10 twist is 100gr shoot the best. What you will get with heavier bullets depends on your rifle. I have six 25cal. rifles(all are 10 twist) and none will shoot 120gr bullets acceptably.
As far as ammo goes, I don't shoot factory ammo,however, my hunting friends tell me that the Remington 100gr Core-Loct is a good place to start.
Five of my 25's are Savage/Stevens two of which are 200's. With just a little trigger tweeking the 200 becomes an excellent shooter. The only negative that I find with the 200 is the 22" barrel,but that is a personal thing and not a deal breaker.
GOOD LUCK and GOOD SHOOTING!!!