May I wish you a warm welcome to the CameraLabs forum.
Having made the reverse transition (from a 5D Mark II to m4/3rds) I don't have any answers but I'll ask if you've already considered and rejected the Sony A7? Same pixel count as the A99, can take A-mount lenses with an adaptor and offers more flexibility in terms of reduced size and weight on those days when you don't want to lug the heavy glass around.
My own journey was prompted by the realisation that I rarely needed shallow depth of field and portability was a more valuable feature. I can still get shallow DoF if I want it (check out Gordon's Leica Nocticron 42.5mm f1.2 review
for example) but I never need the razor thin and almost unmanageable DoF I could achieve with an EF 85mm f1.2 L USM II in front of my old 5D2.