personally, the only thing I see wrong with your rig, is the ram. Most newer PCs are designed to run in dual (or quad) channel, and if I'm not mistaken it's supposed to be 2 sticks of the same ram. For instance, you'd want 2 sticks of 4gb, not a stick of 6 gb and a stick of 2 gb, to make 8. I'm not sure of your config, but I'm almost possitive you could go with less ram, and have better performance from your ram, not to mention 1333 mhz ram isn't ideal for haswell. Haswell "likes" 1600 speed ram the best so it can take full advantage of XMP profiling. As for the rest of the rig, I see nothing wrong. That graphics card should be able to play just about all current games on max settings in 1080p without "much" effort. Crysis might bring it down some, but the 770 is a strong card.
To answer the second bit, the only reason I'd see to upgrade the mobo would be if you decided to go with a 4770k processor for overclocking. The mobo doesn't appear to have pcie 3.0 which could hinder you in the future, if they ever take full advantage of it. Until then I would think that would be a quite capable pc.
If you're missing performance somewhere you might want to look into redoing your system with a fresh installation of windows and all new updated drivers. I could definitely see the RAM causing issues. If it's just "seeming" slow, a SSD, for bootup and a few games, would be a nice investment over a new mobo.
If you look into getting new ram, I'd suggest G.Skill 2x4gb. I have 16gb (4x4gb) and I love them. Make sure they're 1600 speed.
If you decide to go with a SSD, I'd suggest a samsung 840 evo or pro in 128 gb or 256 gb, depending on your storage needs.