Dual channel or single channel does not make a huge difference. What is important memory wise from most important to less important considerations to make when buying and setting up memory. Anyway, to me this is kind of the checklist for buying memory.
1 You have enough memory. No matter if dual channel or how fast it is, if you don't have enough, Windows starts using the swap file on the disk. The fastest most optimized dual channel memory in the world is useless if Windows has to start using the swap file.
2. You have the right memory speed. This is a very broad and flexible consideration though, the right memory speed and timings is greatly dependent on the processor and platform you are running, and what you will be doing with it.
3. Dual channel mode. This is the optimum way to run memory, but we are really getting down to small, small difference's now. You will probably only see the difference here in benchmarks. Take this into consideration after you have zero'd in on the first 2 steps. But, with memory so cheap these days, and knowing what you know now, there is simply no reason that anyone should be running odd ball sticks and sizes. Buy memory in matched pairs and you don't even have to think about this one.
4 If you are you are running a Phenom Processor, there are some additional considerations. A Phenom has 2 memory controllers, and for most things the average person does, including gaming, you get better memory performance by running your memory unganged. This allows the 2 memory controllers to work independently from each other. If you run them in ganged mode, the controllers work in series rather than parallel, and one controller must wait on the other one to finish what it is doing.
1 stick single channel, 2 sticks dual channel, and 3 sticks back to single channel on a dual architecture board. So if you use 3 sticks you are actually slowing down your memory.
The performance loss of single channel is negligable...
As expected, the performance difference between single channel and dual channel DDR2-800 memory using an up-to-date Core 2 Duo system Compare Prices on Core 2 Duo Processors is little to nil, depending on the benchmark - most tests show differences, but they are really small. For games and enthusiast PCs, we recommend sticking to high-performance dual channel RAM, because the memory is one of those components that you want to perform best for a smooth experience. For regular applications, though, it doesn’t really matter much whether you run single or dual channel. Two 1 GB DIMMs typically are cheaper than a single 2 GB module, but a single DIMM will reduce your power consumption by several watts (which might just be more interesting than it is important).