"7.6 by 31 (120L)would be stable and hold in more solid, hollow stuff for a 90Kg ish dude?" - yes.
However, depending on your level, it may become too big if you want to surf vertically in the pocket. No "survavibility" problems, but tightening turns in 15s overhead swells becomes tricky for my 95kg. I i am getting also the same shape in 7'3 x 29"3/4 x 105l for powerful conditions, the 120l being surprizingly fun also in small waves (at least waist size).
Here are 2 vids of my 95ks on the wide-nosed Gong Fatal 7'5" by 31 (120L):
One on glassy but unclean conditions, where you see that this kind of shape can handle waves flattening out (high tide, too much water) or suddenly hollowing a bit
One where you can see how the wide nose allows to take off really early by leveraging it, but the width is a bit too much to handle at the bottom: you can tell because my body is more leaned in than the board is banked, the sign that I am not totally commited in the turn. I think it is because the outline curve means that banking it will make it turn quite sharply, and I am not yet familliar enough with the board to anticipate what it will do, so I "chicken out". But I had no issue surfing these waves and holding in the face, just could not (yet?) commit in turns as in slower waves.