Interlink Communications. London
I own and use all three of the Sony's mentioned. In my experience it depends on what profile you're shooting. If in S-Log then you'll probably need a Shogun or equivalent on the FS5, it just can't manage the profile internally on the SD card. The A7 gives you some nice options with the form factor and large sensor so this is a real contender.
I currently own FS7 and FS5, the EVA looks very impressive. Dual ISO and the higher data rates are very appealing, the official film looks so good- but then they always do.
Not sure it has enough features to make me part with the Sony's just yet though???