The Fractal case that I suggested is 5" shorter than your HAF X, and the HAF XB (you named it as the HAF LAN) would work too. Neither would have any problems with the psu, there are a few different standards, and both cases should easily fit any psu you have (but to be on the safe side, tell me what psu you use, and I will just make sure, as well as make sure that you would have enough power for the Red Rocket as well).
Secondly, Ivy Bridge refers to the generation of processor, and you do not have Ivy Bridge, you are using Sandy Bridge-E (note the E, it means enthusiast and it is a much faster and also a larger cpu socket. It uses 2011 and Ivy Bridge, the non mainstream chips use 1155). When you are looking at motherboards, I want you to look in the name of the boards, it should say X79 somewhere, or it will not be compatible with your cpu. Motherboards have a chip on them (kind of like a mini cpu) that will control a few things like usb, etc. as well as control the cpu) and socket 2011/Sandy Bridge-E uses a chip called X79, the Ivy Bridge uses a chip called Z77. So if a motherboard says Z77, it is not compatible.
I do not wish to confuse you, but this does need a bit of clearing up. The successor to Sandy Bridge-E will be called Ivy Bridge-E and will also use 2011 and X79 just like Sandy Bridge-E, that is where you got the idea that the "upcoming" Ivy Bridge cpus would use 2011.
When they say a board uses x16 x8 x4, they are referring to the amount of pcie lanes being used by each slot when there is a gpu in all three. Every cpu has what are called pcie lanes, these are simply lanes from the motherboard to the cpu, and different generations of cpus have different amounts of lanes. The Ivy Bridge cpus have 16 lanes, and there are different kinds of slots on a motherboard. The big slots are x16, so they take 16 lanes, but when you have two slots populated, the cpu can only give 8 lanes to each slot. Then when you put a third in, the cpu would give 8 lanes, 8 lanes, and 4 lanes (the extra 4 lanes are from the southbridge chip). Please! do not worry about this though, this is the simplest explanation to try and put it out of your head. Because you have a Sandy Bridge-E cpu, you have 40 lanes and DO Not have to worry about any of this. It is no problem to you. An extra little tidbit, the upcoming Ivy Bridge-E (note the E) will have 80 lanes! This kind of stuff will confuse you, I promise, if you do want to learn more, wait a bit until you have more of a base knowledge of how stuff works as this is quite advanced and I gave you a very simple breakdown.
Your current motherboard will be able to handle the third gpu, the red rocket, by the way. It does have the three x16 slots that you require, (one will run at x8, which is half the bandwidth of x16, but no gpu at this point, not even the red rocket would saturate that amount of bandwidth so there is still no need to worry).
And on a personal note, I have been sitting here wondering why you would need so much processing power, and then also a red rocket. What do you do for work that requires that much horsepower?!
I really hope this helped, sorry for the long answer, but there was a lot to address
Austin