It doesn't even have 6-8kg of inherent buoyancy... or I wouldn't be able to dive it with 7kg and 2 aluminium tanks . You're also unlikely to have a suit compressed to 0 volume. So I'd rather take a guess than oversize it, thick neoprene doesn't belong below 30m imo anyway.7mm wetsuits can lose quite a bit more than 2KG of buoyancy when fully compressed, probably more like 6-8KG. The most conservative way of determining your wetsuit's potential buoyancy loss is to put it in a mesh bag and see how much weight it takes to sink it. This is it's total buoyancy, and cannot lose more than that amount.
Please explain how I can use a failed BC? Some don't use droppable weights (I'm of those, and don't consider myself in danger, ever. I wouldn't need the BC to get my ass up), I also don't want to fiddle with those ****ty weight pockets some people think are so handy. PADI recommends using your own BC when getting someone up... I recently quoted that somewhere else, page 166 in rescue diver manual...Please do not size a wing with additional lift to assist another diver. Rescue protocols specify using the other diver's own BC, dropping weights, or a combination of the two. There was recently a big thread on this very topic.
But that's off topic, so I'll leave this here and let Yoyoguy decide for himself...