I would rather pickup a used OM-D.
I already have an OM-D which I like except the handling, even with the grip, it so small which I guess for some is a good thing.
I actually rented a GH3 just to see for myself how much bigger it was compared to the OM-D with the OM-D grip attached, they both weigh the same thing, which I was surprised by, yet the GH3 IMHO does handle better and you don't need the battery grip, which on the OM-D I think it's a must.
Yet on the other hand at least to me, the OM-D does feel more solid, less plastic and the EVF I prefer much more on the OM-D, though what I found really interesting on the GH3 is in manual focus food, it zooms in and utilizes the whole EVF, no cropping, very interesting and then the EVF looks a lot better.
I was hoping that the G6 would be a stripped down versio of the GH3, not so video oriented, but still have good body handling. Oh we'll I will stick with my OM-D.