Ram questions

Hello everybody
So anyway I ahve a few questinos regarding RAM for building my PC

Whats the difference between 1333 vs 1600 MHZ RAM Performance wise? Should i bother with 1600? I mean is it worth it if its going to be a problem for me to get that vs the 1333 model?
And well you see atm i can afford 4GB Ram.. Now My Motherboard has 4 slots
So my two options are 1 x 4GB or 2 x 2GB
Now i want to take 2 x 2GB To take advantage of dua channel.. but I will probably upgrade in a month to 8GB
So I thought if i took the dual channel, Id have to get another 2GB Which would fill all myslots (4x2GB)
But If I took the single 4GB Now, considering that its temporarily and I will be adding another 4 soon... Would I see a major decrease in performance vs Dual Channel? 

Well it is worth it to go from 1333 to 1600 but you have to make shure that both have a low cas latency and a voltage at or under 1.5 V


Hope it helped!

Thanks, Looking for more answers :)

I have DDR3-1333 and i have OC it to 1600, there was zero performance difference between them. Unless your system uses a APU or you have a serious high end gaming/editing rig(and you want to OC to the moon), i can not justify buying fast ram as you will never notice it. If you can get DDR3-1600 for lest say a few coins more then DDR3-1333 then please do buy it, but if the price difference is a tank of gas or a  couple of meals don't bother.

You can run a single 4gb stick in a dual channel, the performance difference between single channel and dual channel at most will be 5-10% in gaming. Toms hardware did a test on this with DDR2 memory, and i think the average loss was 2% through most of the applications. Here is the link: http://www.tomshardware.com/reviews/PARALLEL-PROCESSING,1705-11.html

Like waffle mentioned, you want a nice low cas and 1.5v at least in your memory. SIngle channel vs dual channel mode most likely will not matter anyway since you will be adding that second stick a month after. Quality ram is better then quantity.