Hi guenthermat,
In most Testing Centers, the laminated pad is legal-pad sized and 6 sheets (and you can write on both sides of each sheet). The front of the first sheet has instructions written on it, so you essentially have 11 'surfaces' to write on. That is a LOT of space - and if you were organized, then you could probably take your entire GMAT on just one pad. That having been said, you can exchange your pad for a fresh one (you will have to trade pads though - you can't have 2 pads at once) at any time - including during your two 8-minute breaks. Thus, the smartest time to make that exchange is during a break, when you won't have to wait for the moderator to come to you (while your Test clock is running).
GMAT assassins aren't born, they're made,
Rich