Sierra matchking 168 with 46 grains of Varget start with 45 and work up.
The hottest data I've seen is 46.0 Varget under a 168gr MK. That is from Hodgdon and is a maximum, compressed load. I tried 45gr under 168 SMK in R-P and Federal brass and it was shaving a shiny ejector circle on the casehead. Just as importantly, it wasn't shooting that well for me. I backed down to 44.5gr in my last 20 and had the best session so far. I've heard 44gr quoted often as a very good load. That is what I'll load tonight.