I agree with Rolli59; If you upgrade your graphics card, jump a couple of tiers in capability. If you do not, you will not notice much difference, and be disappointed. That means a GTX470 class card.
CPU chips differ in their ability to be overclocked. Yours may be one of those that are only average.
How important is cpu power to what you do? When the 3.0 OC was working, did it make much of a difference?
You might look on e-bay for a different chip which might OC better. Your Q9300 should fetch enough to offset much of the cost.
That said, I think I would not invest in a pc that was near two generations old, and start saving up for "sandy bridge".
It should launch in January.