Which mirrorless camera are best suited for focusing (manual is OK) and framing in low-light? I have an Olympus e-pm2, and I can't see anything on the LV when its really dark, and have to resort to tricks and guesswork to get a 2sec iso 6400, f4.0 photo properly focused. Basically what I'd like is a very sensitive LV or EVF and on-screen focus assistance such as distance and DOF display (I think Fujis do that)
2 seconds, f4.0 and ISO 6400... You must be in a really dark environment, there. I'm not sure if there's anything that'll be bright enough for that type of lighting environment when in live view, anyway.
However, the Olympus have something called a Live Time feature. It only works in bulb mode but might be something you're after.
Both the OM-D E-M5 & the E-M1 have this feature. They both have a DOF preview as well put probably won't work in low light conditions.
EDIT: You might find that the FujiFilm/Sony A7/A7R are only slightly better than the OM-D.