Buy a 1x4GB stick
Replace my current 2x2GB with 2x4GB
Reorient my heat sink fan (which will mess up my air flow) to accomodate 4x2GB.
Option 1 is the cheapest and least wasteful, but I seem to recall that RAM works best in matching pairs? Will it be ok to run a 4GB stick that is different than my existing pair of 2GB sticks? This PC is used for lots of gaming, but I usually don't overclock anything, if that matters.