I have had the 7'7 Pro for the last year and I recently got the new 7'4 Pro (about 3 weeks ago). I weight between 76 and 78kg and can ride them both. They are both extremely good boards and I thought I might do a comparison on them both.

So firstly, the 7'7... This board has 92L and is 27 wide and 3.8 thick. It is really good at accelerating and really stable thanks to all of its volume. It is really good at popping up on the waves and is also good at rail turns and slides... The Starboard website recommends that max weight of 70kg (My weight: 78kg)
The 7'4.... This board has 78L, a width of 25.5 and a thickness of 3.5 (that is the thickness written on my board). I find it to be a lot less stable than the 7'7 and it is mostly submerged under my bodyweight and if I stop completely then it is at least ankle deep (which I have no problem with). The Starboard website recommends a max weight of 65kg (So I am 13kg over weight limit). I think that this is honestly the best board I have ever used. It is really fast, it rail turns well and slides well and it can foam climb a lot better than the 7'7. Getting air on this board feels great as it also does on the 7'7 and I think that I can get more air on the 7'4 because of the speed. I think that the 7'4 is better than the 7'7 in almost every way except for stability and also that is makes me more tired/hungry (I get hungry in general anyway haha)
Both these boards were hard to use for the first 2 days and now I can stand on them with ease in almost any condition including chop and wind... Currents are usually fine with these boards but can still get me if it is strong enough.
In my opinion, the 7'4 is a better board for good days, the 7'7 is a better all rounder but you need to be confident on the 7'7 before even considering the 7'4
Here are some pics of the 7'7:
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Here are some pics of the 7'4: