EDIT: I should have written:

"So the question is: Do I add 2X 4GB sticks to what's there and use it in two channel mode, or do I just scrap it all and buy two kits from Crucial...a 12GB and a 6GB and use it in tri-channel mode?"

Also, I noticed the Dell RAM is 1333MHz, while Crucial only has 10600MHz or 12800MHz. Will the speed difference be significant...again, for Photoshop work, not gaming? My goal is to have 2-3 programs such as Adobe Bridge and LightRoom open while working on 500~800MB photos in Photoshop without slowdowns.

If you have a multiple of 3 sticks of RAM it'll operate in tri-channel mode. Adding 2 to the 4, will make 6 (try to keep up).

There's two different ways of indicating RAM speed. One is to identify the way the clock is read (DDR/2/3), and the clock speed 1333 MHz. The other is the "PC" speed, which combines the different data-rates with the clock to give an over-all view of how different types of RAM compare to each other. DDR3 1333 is the same as PC-10600.

The motherboard is tri-channel with a less-than-optimal dual-channel fallback capability. You'll notice that all the tri-channel configs are evenly divisible by three. Since the 8GB configuration comes with 4x 2GB DIMMs and there are only six slots, you'll hit a max of 12GB if you don't want to "waste" any of the memory that came with the computer. You need to have triplets of the same size, for optimal memory performance. 16GB is sub-optimal.

Thank you both. I understand the multiples of two and multiples of three part. I just wasn't sure that this particular build wouldn't be dual-channel instead of tri channel.

Before purchase, when researching dual channel v. Tri channel, it didn't seem like the difference was all that big.... but it also seems the posts I was finding were 1-2 years older.

Is tri-channel reasonably faster than dual-channel in real world use?

So, ideally, with four existing sticks in the coming PC, I'd throw away one stick, leaving three remaining. Put them in the (for example) 1-3-5 DIMM slots.

Then, I can order, say, a 12GB/3-stick combo from Crucial, put those three sticks in the 2-4-6 slots.

That'll give me 18GB total, with two sets of three matched to each other. My understanding is that two sets don't need to match each other, as long as the three sticks within each set do.

Chances are you can add two Crucial sticks, and suffer no ill effects. You'd probably want to run Memtest86 http://www.memtest86.com/ to check for errors (I do this on every new machine anyway). As long as the sticks have the same basic specs you'll be fine.

But yeah, dropping one, and adding three identical would be ideal. But ideal isn't always needed.

Awesome! Thanks Chris!

The Crucial kits don't actually save money either. If you buy individual sticks you can save a penny on two, or two cents on three! So if you do end up with errors, you can pick up the third stick (just use the part number on the one you get out of the kit) and not be out any extra money (except for the Dell stick you threw away).

What kind of CPU does this thing have? If it's a 9 series i7, then you want triple channel, no question. No way would I do 9 GB, though (6 DIMMS? Haven't these people heard of 4 GB DIMMs?) What awful config choices.

great- thanks Chris!

Is Crucial a preferred brand? I was also wondering about Corsair or G.SKILL from Newegg?

For instance, this set seems highly rated, less expensive and (I think) should be compatible (unless I'm missing something like the Cas latency or Voltage differences or something).