I finally settled on 15/48, which seems to be a real sweet spot for my riding. I went through a stage of 16/48 (i.e. equivalent of original 15/45) for a trip to Bots over Easter, but have battled going slowly on the pans off the flooded main tracks on the grassy plains with tons of rabbit and aardvark holes. I did carry 15 with me but was lazy to change it.
I did change it afterwards as I was doing De Wildt every weekend, and it really is great allround ratio for me. I can do slow stuff, but surprisingly it is sweet even for a fast dirt roads (no idea about speed as my speedo/revmeter packer up already in Moz) where the wide spread of power allows me to stay most of the time in 6th, only occasionally going down to 5th in deep sand. And the bike is very responsive throughout.