Hi Guys,
Both good questions - so I am between 76-78kg´s, my general waveboard is the Grip 82 if I have to choose just one for a place like Cape Town with it's big range of conditions/mainly stronger winds. When we tested the final Mamba 84 prototypes, we had a variety of winds, 4.2 and 5.3 probably the most used size sails - and there the Mamba 84 showed the extra range with the bigger sails, vs the Grip 82. But it's also great with a 4.2 and substantially better in side shore/choppy waves than the previous Stubby 82. So I think for Mourillon's weight this is fine and will fit very nicely into your quiver for sure with the other 2 boards.
As for Daithi, being heavier, I think you'll like the bit of extra volume which is always nice - and for sure the range in stronger winds with the smaller tail is better on the Mamba 94 than the STB89, this is something we specifically cross tested, as per usual. Not sure how windy the spots are where you sail, but if it stays at around 4.0/4.2 conditions, you could also consider the slightly thicker Grip 86 as your second board, feels just like the 82 but blown up in the thickness for more volume. Even with my lighter weight I love that board with a 5.3 for example, vs the classic 82 which is then just on the limit with a 5.3 if the wind is light? and also works well down to 4.0/4.2....still a pretty big difference between Grip 86/Mamba 94, but depends on how many high wind days you have. I just always like a bit more volume as I get older, especially with the multi fin boards this is not a problem. I used to have 4 waveboards and tried to get onto the single fin 68L as quickly as possible..:-)