Advanced legacy lens user: What to choose Olympus OM-D E-M5 or Sony NEX-6?

Remember to consider properly the fact that Sony's bigger sensor implies a lesser multiplier in 35mm equivalent focal length. That means that you get more bokeh of your legacy lenses with APS, but also that:

1) Your 50mm FF becomes a 100mm M4/3 or a 75mm APS... and some focal lengths more natural, or classical than others. It's your choice but you most consider the FL of the legacy lenses you have

2) APS multiplier (x1.5) is closer to FF than M4/3 (x2), but anyway, it's hard to find a legacy lens for wide angle, unless you go for bigger and expensive UWA... By the other side, for Super Tele, APS is a joy and M4/3 absolutely fabulous!

3) Again, consider your usual focal length preference, or better, critical situations. If you're fond of long focal lengths, then IBIS is an absolute need!