Unless you need raw CPU power, there isn't much of a benefit of choosing either the Quad or the i7, especially if the dual core has the higher clock speed. Most games are only now taking advantage of dual core CPUs and a few with quads, so in some cases the duals are actually faster. So basically, if you go for the 18.4'' and want the Quad make sure it has a high clock speed. Personally, I think I would take the T/P 9600/9700 over the Q9000. And honestly, I don't think the QX9300 is worth the money to upgrade to.
With most games, especially First Person Shooters, graphics power is more important. You would do better to get a dual card set-up than the one with the i7.