You're sure your ram is actually 533mhz? Ram runs at whatever speed you ask of it, and I didn't think 2gb 533mhz sticks exist. It'll be written on the ram. 
You'll overclock higher with 4gb of 1066mhz ram. Otherwise the difference isn't big enough to be worth changing from whatever you currently have
	
		
			
		
		
	
				
			You'll overclock higher with 4gb of 1066mhz ram. Otherwise the difference isn't big enough to be worth changing from whatever you currently have
 
	 
  
 
		 
 
		 
 
		 
 
		
 
 
		