If it sails anything like my Blade, none at all. I have much more weather-helm sailing 2-up than I do sailing 1-up. Although you'd expect the jib to move the centre of effort forward, it seems that this is not a big factor, and what really makes a difference is the increase in forces.

I'm planning to move my mast another notch *forward* next time I go out 2-up.

Paul