Sorry to hold you so long, and sorry th eprevious post wasnt as clear as it should be, it was late here LOL
The main point is that as far as the memory goes, the bandwidth to the computer is a fixed number, so regardless of how many sticks you install, the transfer rate between th ecomputer and the whole of the memory is limited to that value.
Probably the easiest way to put it is that you have, for the sake of arguement, a bandwidth of 100 on memory. Assuming your memory is reasonable in terms od speed, and if it is DDR2 then it is fair to do so, it will use as much bandwidth as it is given, so thememory isnt a bottleneck. Now, when you use dual channel mode, the processor writes to one stick, then immediately to the next stick. Effectively, it puts the first bit of information in the first stick, second in the second, 3rd in th e1st, etc. Because when using one stick, it writes, then has to wait for the memory to write it,so it writes every other time, whereas with dual channel, it uses the time it is waiting for the memory to write info, to write to the other stick. This is th emain reason you see a decent speed boost. Of course, this is offset by other factors, so it doesnt equate to a doubling in speed.
With quad channel, it writes to stick 1, then stick 3, then stick 2, then stick 4- effectively, quad is the same as double dual, although the architecture is slightly different. If your mobo supports FULL quad channel, it works slightly diffeently, in that it writes to sticks 1 and 3 on cylce 1, and sticks 2 and 4 on cycle 2. However, you have to remember that only one thing can be done at a time, but effectively it doubles up. If this were the main factor, then quad could run 4 times as fast as single, but its not.
The bandwidth allocated to the memory determines how much information can be written at one time. Effectively, it determines the maximun number of write operations that can be done in 1 second. So, if you have a bandwidth that allows 100 writes/ second, then that is the most it can handle, full stop. In single channel mode, because it is a write/wait/write/wait cycle, you may find you get (say) 40 writes a second. In dual channel mode, because the wait cycle is omitted, you will double this, so you get 80 writes/second. Now, if you have full quad support, you would double this again to get the max write/read speed, which would be 160 ops/sec. But as the bandwidth limits you to 100 ops/sec, then it will top out at that level, meaning the advantages offered are cancelled because the information going to/from the memory is limited by other areas of the computer.
The other point to bear in mind is that a 2 gig stick can hold more info than a 1 gig, ( I know, obvious!), but this also means that indexing comes into play. When you need to read memory, the CPU has to get the info from the memory. With 4 sticks, it could have to ask 4 sticks if they have the required info, as opposed to just asking 2 sticks, from which to gain info. As such, 2 sticks can relay info back quicker in some cases, due to the interrogation methods.
I hope this explains it a bit better, I have simplified because there is no point going too far into the subject, and i think the post would just be too long. The real question of which is quicker will depend on the timings of the memory, the read/write speed it can theoretically attain, the bandwidth available to the memory, and whether you are multi tasking- this can slow things down due to having various apps using memory, which is why I said before that there is a moot point. The other factor to consider is that with mem ops being so quick, it is other areas of the system that cause bottlenecks, north and southbridges being the prime culprits- there is a limit to what they can cope with in a given time.
Essentially, the choice is up to you, as either way it should be an improvement over single channel. I suggested 2gig sticks because for an upgrade, they will at least have some value, whereas 1 gig sticks may not- more and more mobos are coming oput with just the 2 mem slots. Also there is the imminent acceptance of DDR3 memory ( if/when it happens), which would blow the whole thing away.