System stabillty and/or possible OC

At stock settings it should be stable, if not then you need to return it.

The question of stability only arises when you're overclocking past the manufacturers specifications.

Overclocking will definately be an option if you buy a quality heatsink (not the standard one it comes with). It's on the lower end of the scale as far as quads go, but you could expect 10-20% extra with a decent sink.

My goal with Core2 is always moving the FSB from 333 to 400, but I don't know how easy or hard that is (with regards to voltage options and heat) on the Q8200.

At 400 your RAM will be running as DDR2-800 most likely, depending on what multiplier options are available on the Gigabyte and how well they work (on my Asrock, they dont work at higher FSB speeds).