If you are planning to shift to a new mobo, then you have to get a new processor as well. Core 2 Duo and X58 mobo's dont mix. Also you processor is fine enough. Keep it till sandy bridge comes out, then decide.
Like he said, a new mobo means a new processor.
What would you like this upgrade to accomplish? What is not running as well as you would like?
I also have a Q9450, and no app I use or game I play would benefit in any meaningful way by a CPU upgrade.
Of course, a new mobo may add features that you want, without relying on an add-in card, or may address reliability concerns. Please let us know what is motivating you to upgrade.
Incidentally, though an excellent-cooling case, the CM-RC690 is also a loud case.
I'm not sure what else you might want to add.
Do you have a second hard drive for backups? A decent printer? UPS? What is your resolution? Your GTX460 can handle [at least] 1920x1080. How about a second monitor? A nice chair? There are lots of things that can be done to improve one's experience in front of a PC.