Have you got anything to watch the 4k footage on? Also have you looked at the recording time of the black in 4k? It's poor, very poor. My 4 silver will film in 4k, albeit at a lower FPS....not that I've tried, battery life is poor when filming at 1080p (probably 1:30 video time and that's with wifi off). The touch screen is a great feature and definitely worth it...
My advice would be to go 4 silver and buy a few extra batteries.