I haven’t tried Varget with 123s yet but it works VERY well with 130gr AR Hybrids, clocking at 2868fps from my 24” Bartlein barrel. I did a 10 round load work up with .4gr between charges, looking for nothing but pressure signs. By the time I got a faint ejector mark, velocity was crazy high, so much so that I won’t repeat it here. All ten charges went into a group that was about .7”. With the load I settled on, .3s and .4s are the norm and .2s are fairly common. Pic below is the most recent group I put on paper. It measured .291”
Anyway, if I were you, I’d start at about 37gr, and load 10 rounds increasing .4gr per charge and find the max for your rifle. After that, do your normal load development routine. I’d be very surprised if you didn’t come up with a load that bug holes. You don’t hear about it much but Varget works great out of the 6.5 Creedmoor with bullets up to 130gr.
John