If your in a strict budget situation, that's when you go with the lower amount of ram and add more later. But keep in mind you may have to replace all of your sticks. I usually have luck adding more ram if I don't wait to long after my initial purchase but if I wait to long...the make and model ram disappears or gets changed in a way it won't work with my original set. So I am stuck replacing all of it. Also if your a ram overclocker or use pre-overclocked ram like myself. You never want to run more the 2 dimms in a dual channel set-up and more the 4 in a quad channel set-up if you can avoid it. You OC potential can drop pretty hard sometimes, others you get lucky. Again you can be forced to replace it if you want the faster speeds. I and face these issue frequently. My server's ram is not OCd so I can use all the dimms and upgrade. It started with 8GB and now sits at 16GB of at DDR3 1600mhz. My wife's CPU never OCd great with ram (past 1600mhz at least on a 1066mhz CPU...some folks hit 1866mhz on that CPU and higher) I was lucky could pull DDR3 1600mhz out of all 6 dimms (i7 970 a ti-channel CPU). It started with 3 dimms at 12 GB and ended up at 24GB. Just added more of the same make and model. My rig I simply populate 4 dimms but when I upgraded from 16GB to 32GB this year. I didn't get the chance to try and pull 2400mhz out of 8 dimms. My ram model changed and I was forced to get all new ram. So these are the risks you will be taking. You may have to lower speed if you OC...you may not...and you may have to buy all new ram if your make and model is changed in a significant way or is discontinued. I urge folks to get as much ram as they think they will ever need when purchasing unless these are risks they are willing to take or their budget, in cases like yours, strictly dictates otherwise. It isn't perfect but it will work for now.