I borrowed some L pro Canon glass to play with, so I tested it against the GH1 and its Sunday best.
Both cameras at base 100 ISO, fast shutter (sun!snow!), handheld from ca 25m from the focus plane, several shots taken and the best picked, LR 2.6 raw no tweaking. My usual garden view which is fairly challenging: sun and snow and contrasts. Focus on the double red-yellow swing. Crops from GH1 are 100% 1600 pixels wide, the 5Dm2 got a preferred treatment by downsampling from 21MP to the same crop (ca 2:1).
Here I compared wide/fast glass. 5Dm2 sported: 24mm/1.4L II and 24-70/2.8, GH1 wore Schneider Kreuznach 10mm/f1.8 c-mount , lumix 7-14 and lumix 14-45. All glass at/around 24mm FF or equivalent , wide open and then slightly closed down. You can read pix descriptions with mouse covering and EXIFs are there too.
Next I'll test around normal f-lengths (50mm FF) and finally a slight tele.
From left-right and then top-down:
1) full view 24mm FF 2) GH1+SK 10/f1.8 3) GH1 + SK 10/f2.8 4) GH1 + lumix vario 7-14 at 12mm/f4
5) GH1 + lumix vario 14-45 at 14mm/f3.5
6)5Dm2 + 24-70/2.8 at 24mm/f2.8 7) 5Dm2 + 24-70 at 24mm/f6.3 8) 5Dm2 + 24/f1.4 at f1.4 9) 5Dm2 + 24mm/f1.4 at f 2.8