I started off with 120 grain norma/nosler bullets like you big ears, out of my t3 swede. I know use 140g sst and have found that they group just as well and to almost the same point of impact, so i wouldn't worry too much about the variant in bullet weights, although saying that it could obviously be different in your rifle. Unfortunately i dont have any load data for the 123gr, but i would say just experiment with all different weights until you can find something which groups well and that you like.
Just my thoughts!
Cam