I suppose the board could be holding you back a tad. I think that is only a 4+1+1 power phase board. If you are getting your 4.0GHZ by increasing the voltage, try setting the voltage to default and just upping the multiplier to 40. See if anything changes in your Fire Strike bench.
You could download/run 3DMark Vantage. It gives both a GPU and a CPU score. That way, we could compare our CPU/GPU scores to see which one is lagging.
Also, (and this is just a hair-brained theory on my part), I always wondered if a Z77 board being optimized for Ivy Bridge processors is a bit UN-optimized for Sandy Bridge.