I'm pretty sure ISO 1250 will be fine for a digital RF.
I never got the fuss about the ISO sensitivity on the M8. When I shoot 200ASA film, I rate it at 160, 400ASA rated at 320, etc. ISO 1250 is the typical rating for 1600ASA film.
The 160 ISO setting on an M8 gets you shots that look like 200ASA film exposed at 160.
Like with film, 1/3 stop over-exposure is a good thing with RAW. Easier to correct over-exposure and that way have saturated pixels toned down than to under-expose and brighten up those pixels with rainbow colors, adding noise in the process.
Those asking for faster ISO speeds generally do not know their (film) basics, IMHO.
Leica themselves have never proclaimed it, but I feel their opinion on shooting with fast shutter speeds in the dark amounts to: If its that dark, you can hide a DSLR in that darkness.
In general, my M8 behaves quite like a film Leica M to me, once I got to understand its philosophy. Save for the bloody filters, which piss me off every time I need them.