Why buy a GH3 over FF

Am considering a change from a Canon 60D to either a GH3 or Sony a99. I like the EVF's abilty to change shutter, aperture and ISO and see histogram with results before fully pressing the shutter button together with articulating rear screen. I read that GH3 has superior video abilities. Any experience in still image IQ printed at 13x17 relative to FF?  How about radio control of TTL flash? (Pocket Wizards seem to suffer from RF noise reliability issues) Also am aware I could come close to purchasing 2 GH3s for the cost a Sony a99 with Zeiss 24-70 lens. What about tethering to PC to bring into Lightroom or control with Iphone? Will shoot 60/40 stills/video.