With the quad core, you will likely be limited by the FSB. My QX9650 doesn't like to go over 400 FSB without going subzero and yours will likely be the same. Since the Q9450 has a locked multiplier of 8, you won't be able to get very far (400 FSB = 3.2 GHz). If you can get it to those speeds, it will be an upgrade. Obviously, this depends on a lot of factors. I don't know how the chip will overclock, how good your board will handle it nor if your cooling can handle it.
What you run on your computer is going to also change the answer. If you only game (which normally only take 1-2 cores), you would be better off getting a real overclock on your current chip. Most had no problem going 4.0 GHz + with ease.
