Need help selecting motherboard

Hello,
Im building a new pc and Im a bit lost in the sauce. I plan on running an i7 2600k cpu with two 6870 graphics cards. So the mother board needs to be able to run crossfire and be a 1155 cpu socket. Im a bit confused about which motherboard will run two pcie slots at 16/16 and not 8/8. To be honest im not even sure if it matters but have read some people saying they are getting errors with their cards because of it. Now I'm also planning on running 2133 ram and that leads to the next question. I noticed alot of boards can run 2133 ram but it says that its 2133 overclocked. Does that mean i can run standard 2133 ram or do I have to buy 1600 and over clock it? I plan on overclocking the CPU and in the future run a solid state hard drive for the operating system/games. Also is the new pcie 3.0 worth getting or does it not give any performance increase? Another question I am not sure about is whether i should be getting a z68 or p67 northbridge? I'm not sure exactly what the performance increase would be from the z68. I'm trying to make a PC that gives me the best bang for my buck so if anyone can find a motherboard for me within the $125-$200 price range that would be great. I am by no means an expert at any of this but have built a few comps in the past and look forward to the new project. I am on a bit of a budget so the closer to $125 the better. Although I dont want to put myself in a box because I enjoy to tinker. Any advice would be greatly appreciated.