I went with an XTR shifter and XT derailleur with my new bike. 46T Sunrace cassette works good with the combo.
So my front ring is 30T, seems like the right ratio for riding in snow, may be too low and lack some high gearing, but it's a fatbike after all, who am I chasing any ways? lol
On my other fatbike I run a 1x10 SLX setup with 42T cassette and 30T chainring. In deep snow, I'd often run out of gears. If your crank is direct mount, consider a 28T front. Looks tiny, but if you plan to do any significant climbs the extra lows will help. Only negative are the bigger jumps between gears.