Well, this topic keeps on popping up.
I can tell you about my experiences with the IS87.
It's a super easy board to ride. Nothing technical about it and I'm no pro.
I use it with 5.0 and 5.7 sails.
It flies over chop and if I have to, I found it not too difficult to jump as well.
If you take a look at the dimensions of an IS87, a Kode 86 and a Kode 80
IS87: Length x Width x Tail Width: 243x56.5x36.6
K86 : Length x Width x Tail Width: 237x58.5x38.3
K80: Length x Width x Tail Width: 234x56x33.9
They are all not that far apart.
The tail of the K86 is even bigger than the IS87, which should make it even harder to control in heavy conditions.
The biggest difference has to be the rocker line of these boards.
This is important when you start riding waves.
If you're not into this, I recommend an IS87.
Personally I'm now considering an IS80 (same dimensions, lower volume), just like Remi advised a couple of months ago.
The IS87 only helps in serious lulls.
And if hell breaks loose, an old school wave board is probably the best choice. They are still the smoothest in these conditions.