While moving to a IB/Haswell will be an improvement, I doubt you'll see a lot of difference in real life. My 2nd machine is a i7-875K @ 3.6GHZ w/2 x HD 7870 OC cards. It actually keeps up in games with the rig in my sig below. And posts a nearly identical 3DMark Vantage overall score.
Its running most games on high setting but the fps is about 50 ish on average. the big killer atm is rome 2 but obviously there is alot of problems with that . Also when games like battle feild 4 ect start to appear I have a feeling it will struggle to get 50+fps on high settings. Guess I am trying to "future proof " this rig for the next gen of games that will be with us soon thanks for the help
You may want to add some more RAM. While 4GB is sufficient for games (games are still 32 bit coded and can only access 4GB memory), the OS uses a bit for itself and overhead. I'd go for 6 to 8 GB.
If you still feel a new CPU/MB is the answer, I would pick a SB/Haswell i5-xxxK processor and look into a good Asus, Gigabyte, or Asrock board. But I don't feel the difference you'll see would make be enough to warrant the cost... unless you just WANT to upgrade.
Do you have a lot of stuff running in the background? Look in the Windows tray and see how much stuff is running. Then open System Configuration/Start up and see how many boxes you can uncheck. I rarely have more than 6 -10 items checked. And most of them are by personal choice.