Hello,I currently have 2 sticks of 2G DDR3 1333 mhz ram in my PC. I'm going to purchase 2 more sticks of 4G from newegg (also 1333mhz). Would it be better to run all 4 sticks at once (2 2G's and 2 4G's) or only the 2X4GB?
It's never recommended to mix RAM - even of the identical model as it is NOT guaranteed to work without issue. The only means to be sure that multiple DIMMs will function without problems is to buy ONE matched, tested RAM Kit. With the current low prices on RAM I would suggest you buy ONE matched, tested RAM kit of the full quantity you desire and NOT mix in any of the RAM you have. While some folks have successfully mixed RAM many have found it impossible and a waste of money.
Always pick RAM that is approved for the specific brand CPU you are using as not all RAM works with all CPUs. 8 GB. of RAM is the ideal for most people. A 2x 4GB. kit is around $60. on Newegg depending on speed and model.
If you can't buy another pair of 2GB like you already have then the 2x4GB is your best option. If you wanted you could try to run the 2x4GB with your original RAM and see how it goes. If it passes memtest a few times it should be good to go.
Though as stated above 8GB is generally enough for most people so unless you need it, it may not be worth your trouble. Also I was wondering your reasons for upgrading to 8/12GB? 4GB is often enough for most people.
for a average end user that is looking for more performance and quicker load time more memory is better when overclocking at competition and things of that nature 2 sticks are better because of what the requirments are like super pi and other tests that don't apply to an average end user when they are trying to load media or edit photos. But super pi does apply to that when you are a experienced computer engineer. Sometimes you have to let professionals handle the workhorse end of the business tho.