OK ALL YOU full frame camera fanatics

First it 2 stops not 1 and 1/2.

For all formats and exposure, F/1.4 is F/1.4.  Only with DoF will F/1.4 on 4/3rds look like f/2.8 on FF.

For your real problem compare the D600 @ ISO3200 or ISO6400 to the E5.  Notice how good the D600 RAW files look and can you see the deeper color range?  If you try pulling highlights from shadows you will also get a lot more.

Now if you never go above ISO800 with the E5, you will be fine.