My pc is around the same specs as yours, maybe abit more powerful....
Intel I7 only o/ced to 3.5...
HD 5870
8GB of 1600 MHZ ram
Plus plenty of fans in my case
I wouldn't call this a "high end" system, but it seems to struggle most when shadow's are turned on high and bloom (bloom and motion blur i auto check off, there crap anyways).
On most games shadow quality always seems to be the laag point. Maybe you should just turn them down and see what happens. Im not to worried personally, ill be getting my 2600k, HD6950 and maybe with a new mobo and water cooler for under 900$.