I have 4 data points on A cat sails.

Contender AK3 with Fiberfoam battens 4kg.
DP KX06/04 with Fiberfoam 4kg
Bimare 2005 xj main with Fiberfoam - 5kg
Bimare 2004 xj main with Fiberfoam - 5.9kg.

2kg sounds pretty thin....

Remember, most sail makers will built you a sail on the heavy side to be safe. You can't see it stretching and losing shape, but you can see it rip and wear. My personal opinion is that a lighter sail is better because sails stretch, and shrink from day one...so a sail built out of heavier material will only lull you into thinking the sail is still in good shape long after its a piece of crap.

Go with Kevlar, its going to fail (rip) instead of stretch -then you know its time for a new one.

Bill