Is it the Leica? Haven't tried that one B4. On the side note, why wud anyone wants to shoot a group shot at 2.8? Personally, i use 4 ~ 8 juz to be sure everyone in the shot looks sharp even on the 4/3 cams. I did some coverage for events b4 & its like a lecture hall size & full of people, i was on the stage, also use F4 on the 14-54 le, not 2.8 cos the DOF juz can't cover.
But i believe the bottom line is that every brand has their lenses optimised according to their sensor & technology integrated. This is the reason why there exist diff crop sizes & none looks bad at all. I personally dun believe there's one no.1 brand around.
Back to cosycatus comments on ambient light with 2.8, i think u can also get ambient light with F5.6, its a matter of balancing the DOF, ISO, shutter speed & lightings. If i had done it in F5.6 with ambient lighting, i dun see why only 2.8 can give that result. :think: