My 670 is at stock, admittedly it's an FTW which has factory OC, but the OP doesn't say what sort of 670 so it may also be a FTW or similarly factory clocked card (did they make 4GB reference cards?).
Regarding the CPU, that could well make a difference, although I'd imagine it's the hyperthreading that would help as much as the clock increase if BF4 runs ok on AMD CPUs.
CPU makes a huge difference.
http://gamegpu.ru/images/remote/htt..._GPU-Action-Battlefield_4-test-bf4_proz_2.jpg
40-50 on ultra sounds about right with an i7, but an i5 is not going to cope as well.
 
	 
  
 
		 
 
		 
 
		 Occasional drops to 50FPS but still an extremely playable frame rate! Quite chuffed with my little system
 Occasional drops to 50FPS but still an extremely playable frame rate! Quite chuffed with my little system  
 
		 
 
		
 but this is overclockers i'm sure 99% of us OC our gpus without even trying stock
  but this is overclockers i'm sure 99% of us OC our gpus without even trying stock