My wife recently got a new Tikka in 270 Win. She tends to like the 110TTSX and 129 LRX, so 10" twist has been fine. I have my eye on the Hammer Hunters at 156gn and 168gn, should she want to do elk with that rifle. That last bullet has a BC of G7 .266 from one test and .309 from calculated shot drops. Not too shabby.
However, if I/she were to rebarrel her rifle, I think that I would recommend a 7" twist, since the 168gn benefits from a 7" twist. McGowen in Kalispell does such barrels, for one.
As mentioned, the 156gn can use the 8" twist and you can calculate differences in drop and windage for both bullets. The extra speed (100fps?) on the 156gn may be all that is needed inside 500 yards. I think that windage for both will be about the same at 400-500 yards, while the 156gn may be slightly flatter, dropping about 2" less inches at 400.