Generally ram does not have to run at its' rated speed but can run slower. But for a board that is spec'd to run DDR3/800 and DDR3/1060 ram, I would not spend the extra to buy DDR3/1600 ram.
The "coming" E-450 is to run DDR3/1333 ram and is one of the changes to the newer E-450, but I have not seen it in retail yet.
All we are discussing here are inexpensive systems when fully decked out to run as a computer inside a case. The ITX boards are tiny. They have no room for a bunch of hard drives to be attached. Most go in cases that would fit up on a shelf in the tV room. MicroATX boards have more board real estate and can have a few more connections, but in neither situation would I have overclocking in mind. It is a buy for inexpensivtivity.
You started the post with/about a cheap0 AMD cpu and we are looking now at a system and that is what we have been talking about after about the second post in thread. Here is a cpu but with video and motherboard for that $100 you mentioned. There is not a lot of headroom in that situation.
Just FYI, the Zotac or Asus would be front-runners in my buying sights.
EDIT: I just went back to the first post and RE-read it. This was said in that first post >> "budget pc just to check email watch youtube brose the web run word and what not" << Well that what not can be the wheel that fell off. If 'what not' is related to any gaming, I would have my doubts about that being doable. If 'what not' is heavy duty video ripping and rendering, I would have my doubts about that being a good idea. Really inexpensive as we have set forth here, gives little room for an expanding/growing "what not". END EDIT.