Re: 167gr Lapua Scenars
So there would be a disadvantage at long range to switching over to the 167 if the 155 Scenar is already working for you. If you are only shooting to 600 yards or so, 168gr loads like Fed GMM are accurate in most rifles.
A 10 twist is not a disadvantage to working up an accurate load for the 155 weight bullets...they will shoot fine out of that twist, but the 155 Scenar can sometimes take a little more experimentation to find the right load and OAL.
If your rifle just doesn't like them try the newer Sierra Palma 2156 or the 155.5 Berger, or any of the 175 gr.
TC