I use a Mamiya Universal (6x9) with a 100/2.8 (a Planar design, which is MUCH better wide open than the more common 100/3.5 Tessar). I use Delta 3200 (no 120 TMZ, sigh) stand developed in 1:1 XTOL for 25-30 minutes, EI of about 12,500. This is a leaf-shutter rangefinder design.

There are a number of other lenses in the system, but none of them are remotely fast. Still, I shoot my 50/6.3 from the neckstrap (and scale focused) as slow as 1/8 with pretty good results.

Plan on adjusting the rangefinder (easy) so your fast lens is dead on--these cameras are very prone to going out of adjustment over the years.

The Koni-Omega is a very similar system, but it lacks the killer-wide-open Planar.

One neat benefit to the Mamiya's slow 50/6.3 is that you can shoot it wide open to get rid of the "spikes" around lights and still have decent depth of field and great lens performance.