Looks like someone is having fun
However, I have identified an issue with your build. Sorry, not trying to discourage you, just trying to help you fix it while you're still early in the build process.
Look at the directionality of the fins on your GPU heatsinks. Then think about the airflow through the chassis. For a reminder, look at the sticker on the CPU heatsink
The GPU fans are going to blow small amounts of low-pressure air upwards/downwards, while the chassis fans are going to blow shitloads of high-pressure air rearwards. What's going to happen is the air moving over the top of the GPUs is going to create a high-pressure zone, preventing the hot air in the GPU from rising and exhausting, and creating pockets of hot air inside and around the GPUs.
For this chassis, you need GPUs with horizontal heatsink fins, not vertical. I mean obviously we always recommend reference design GPUs, but if you're going to go with an OEM design GPU, then you really need one with horizontal fins. You might also find that an OEM design GPU with horizontal fins cools better in this chassis without the shroud and GPU fans, just being passively cooled by the chassis fans alone.
However, I'm afraid that's not your biggest problem, as I do have a bit more discouraging news. We've recently learned that after about a year of continuous use, the R9 290X will kill the motherboard in this chassis. The PCI-e slots will start burning out one-by-one. If you read Tyan's documentation, it states not to use GPUs that draw more than 300W. At stock clocks on algorithms like NTLM and MD5, you'll be pulling around 325W per card. With your 1250 Mhz overclock, you'll likely be pulling around 360W. So if you continue to use this GPU for this build, your motherboard will likely die within the next 12 months.
So biggest recommendation to you is to return these four GPUs that you have, and pick up four GTX 970 or GTX 980 instead. They will be just as fast if not faster and will draw literally half of the power. Then you'll want to use the onboard VGA and ensure that the GPUs are properly spaced out inside the chassis (I know why you did it this way for AMD, but it will not be necessary for Nvidia.)
Good luck!