I don't have a Savage in 223 but I do have a Tikka Varmint with the 1:8 twist. I shoot the 55gr Sierras in mine to about 1/2 MOA with no problem at all. I also loaded up some 40gr which shot OK as well, despite people telling me that they would come apart, they don't.
I have also tried factory ammo ( what a waste of money) 50gr, 55gr, 69gr and 75gr. They all shot pretty well. Should I decide to use a heavier bullet, my rifle shot the 69gr better than 75gr. The others, 5ogr to 60gr all shot about the same. So I decided to keep loading the 55gr as a sort of middle of the road.