I will answer in general on these kind of shapes, as I never tried the ECS 7'11"
In my experience, these slab/tomo shapes should be ridden short. I had - 12 years ago - a 8'11" Tomo, and then a 8'0" Simmons. It was really interesting for a beginner to intermediate level in gentle waves.
But as soon as your technique has progressed enough to attempt to always turn with the rear foot over the fins, they kind of feel like a barge: if you are on the tail, the nose is a long way up front, and the width there is then cumbersome.
So, I am like your mates: at 100kg I have two "slab" shapes in my quiver: a 120L 7'6" (Gong Mob) for weak tiny waves (5s period and less) or when I need paddling speed to flee the crowds, and a 105L 7'3" (Gong Fatal) (with a bit more pulled-in nose & tail) for waves bigger than knee high between 6s to 9s period. On more powerful waves I will use a "performance" shape (Gong Alley) around 8'
I must say that I felt at first that my 7'6" 120L board was too big, but playing with shorter fins allowed my to gain enough looseness on the wave while the extra tail volume make it catch waves nearly as soon as with a 9'.
TL;DR: the ECS 7'11" will probably be too big for you.
I have the 7'5. I am 60-65kg . I mainly surf in small waves at local beach shore break . Nothing bigger than 3ft these days. I love this board . My go too on most occasions .
I had a 7.2 miniun and absolutely loved that board. Mainly in head high to bigger fast down the line waves. Then went to a 8.2 Sunova Speeed which I still use. Great board. I'd love to try the Gong Alley or Sunova flow just to understand what different shape boards offer. Ill follow this thread with interest. From what I understand, the latter boards will be easier to turn without having to get right back on the board and won't compromise speed. Sounds perfect to me.
I have the 7'2 x 28" @103litres JP Slate - it is a great board up to 4ft at which point I want to be on my surfboard... It still goes in bigger, but the tail is huge, you move your feet in transition from bottom turn to top turn to account for this. Pros - 1) it fits in the car, 2) it has foil boxes (added by a friend) 3) it turns so well and can be paddled into small and big waves. cons - it isn't fast paddling, i can't really lend it to my friends who don't paddle.