[Solved] Stupid question about DDR3-1333 compatibility

OK, so I have a homebuilt machine with an Intel DP45SG motherboard and 4GB of Patriot DDR3-1333 RAM. Recently, the motherboard burned out, and after a long fight with Intel over whose fault it was (you can guess how that turned out), suffice to say I am in the market for a different motherboard.

My question is: Will my existing DDR3-1333 RAM work in a motherboard that's only listed as supporting DDR3-1800/1600 (such as this one)? Or is my RAM going to have to be 1600 or higher?

I've heard that if your RAM is a higher clock speed than the board supports, the RAM will still work, just be slowed down by the board. I don't know if it works the other way around or not. Anyone who can enlighten me is much appreciated.

I was looking at the ASUS P5Q3 (specs here). Figured that if I have to get a new board, I might as well go for a slight upgrade while I'm at it. I just don't want to do that only to find that my existing RAM won't work at all.

Alternatively, I guess I could just choose another board that does list support for DDR3-1333, but thought at least having the capability for the higher speed might come in handy if/when I add more RAM.

That also begs the question: At some point in the future (assuming I can get the board issue to work out), if I was using my existing two sticks of DDR3-1333 and added two sticks of DDR3-1600, is that going to cause problems as well? Or am I better off just going with ALL 1333 memory or ALL 1600 memory?