My question atm is, if i add the above mentioned ram, will it create problems in my Rig? or should i just go ahead and buy both new rams?
My current Config is
Processor: Intel core i5 e2500 3.30ghz
Mainboard: Intel DH61WW
Ram: Corsair XMS 4gb x 1
GPU: Power Color HD 6670 -> Going to Upgrade it to GTX 760
PSU: Cooler Master extreme power plus 460w -> Going to Upgrade it to Corsair TX650
Cabinet: Cooler Master elite 310
HDD: Western Digital Caviar Blue 1TB
When upgrading ram it is best to purchase the full amount of ram in a kit which will have matched modules for compatibility.
According to CPU-Z your ram is currently running at 1333MHz (default frequency) enabling XMP should get you to 1600MHz (CPU-Z will report as 800MHz).
You can purchase the single ram module and it may work (just as likely it won't) with your existing ram at 1333MHz and you might even get dual channel function (again the possibility you won't).
Summary: best to purchase all 8GB in a kit