Running twin chainring at the front on my HSD now.
Low range, 38t/21t which is 9.3"-49" then overdrive mode upto 123".
High range 53t/21t which is 13"-69" then overdrive mode upto 172".
The twin ranges work great together, as it opens the range the gears 8-14 work in, so I can stay in the low drag gears longer.
Plus if I hit a short uphill in overdrive mode, I can drop the range for a couple of extra gears before I drop out of overdrive mode.
Only downside is the spider is held on the HSD by a weak circlip.
To much sideways force pops it off.
When the tour ends I'm going to have to improve it's hold by deepening the circlip groove it sits in.