There's no reason to upgrade the motherboard.
The only thing that makes one motherboard better than another is how many I/O expansions does it offer and what "nice to have" features it has. The expansions are more or less a standard. A PCI-Express 3.0 slot on a $400 board will not perform any better than one on a $100 board. Neither will the 6Gbps SATA port. Or the USB 3.0 port. Or the DDR3-1600 slots. Etc. As far as "nice to have" features, it's mostly things like POST codes on a LED display, one-touch overclocking, etc. None of these boost the performance of the motherboard any better than if you did it manually (if the capability exists).
Thanks, I didn't really know that. That will save me some money.