Allow yourself to a treat. The 5DIII will be an giant leap to what you are used to. You will have so much fun with it. And then, when (if...) the 5DIV comes out, you may think, is it worth it?? considering the quality you are getting from the 5DIII? Or maybe, at that time, we have a phenomenal 3D MkI, which will make the combined 1DX/Nikon 800E look like stone age dinosaurs?
The real issue is, ... your motives are passing by you today. Make sure you can capture them when they are there ...
5DIII, 1DX, 8-15/4L, 16-35 f4L IS, 24-70/2.8L II, 70-200/2.8L IS II, 70-300/4-5.6L IS, 200-400/4L IS 1.4x, Zeiss 15/2.8, 17/4L TS-E, Zeiss 21/2.8, 24/3.5L TS-E II, Zeiss 35/1.4, Zeiss Otus 55/1.4, Zeiss Otus 85/1.4, 100/2.8L IS Macro, Zeiss 135/2, 600/4L IS II