EM1 or D600, for Weddings?

I am a wedding photographer who switched from pro FF gear and uses now exclusively MFT gear for all wedding. I can tell you, from my own experience that I haven't encounter any problem or limitation whatsoever, to successfully shoot a wedding with MFT gear, matching and sometimes even exceeding the quality I had with FF gear.
That of course, if you have the right skills and you know what you are doing.

I work together with my wife as a team for all the wedding we shoot. I use em1 and em5 bodies and se uses one em5. The lenses we share are Panny 12-35mm and 35-100mm 2.8, Oly 9-18mm, 17mm 1.8, 45mm 1.8, 75mm 1,8 and Samyang 7.5mm fisheye. We also bring Oly 12-50 kit lens as backup and for close up shots. An Oly 12-40 will join very soon.
Oly flash system works a treat and we use two FL-50r and one fl-600r on or off camera.

All in all we are very happy about the quality and the flexibility of the system and enjoy very much the size and the weight, which is a major consideration if you have to shoot for 12-14 hours on the day as we sometimes do.

My suggestion to you is, as you already own an em5, to go for the the em1. There is nothing to fear about and if you are serious about your photography, and are ready to invest the time needed to build the experience in a new system, you won't regret it.

If you want to read some more opinions on the topic, this is not the right place. Go look a DWF (Digital Wedding Forum) where you will find thousands of excellent wedding pros. It is a paid forum and is not cheap, but worth every Penny.

Cheers
Moti