Bobby,
I have the 2016 7'4 and it feels like 83litres to me (i.e. I don't sink below the water much). Of course it also feels like 25.5 inches wide too so its tippy :)
I was having exactly the same dilemma as you and couldn't get a straight answer on the volume but I just bought it anyway. However, there is a guy on instagram (paddlewoo) who certainly knows his stuff and has both the 2015 and 2016 7'4 boards and told me the 2016 definitely is easier to paddle than the 2015. He even asked Sean poynter who apparently confirmed 2016 = 83litres. However, just so you know... the 2016 still says "78l" on the bottom of it. Mine does...i consider it to be a mistake or they had a load of pre cut graphics hanging around.
Like I said, at 68kg the 2016 7'4 floats me absolutely fine. The width and the narrower nose outline still make it more of a jump from 7'7 to 7'4 than 8'0 to 7'7 though I reckon.