Unless you're willing to get a new motherboard, CPU and ram, I'm thinking you will get the most improvement with the graphics card upgrade.
You shouldn't need to flash BIOS unless you're having issues.
I'll get back to overclocking, running late now.
Motherboards designated VM (value model) are primarily made for the business consumer and do not (usually) have an option for overclocking. You would need a new mobo to overclock in any effective manner.