Just an update, so that others reading this don't come to the wrong conclusions:
I eventually discovered hardware problems related to either the motherboard or the RAM, or the BIOS setup. My RAM didn't play well in the default configuration of the motherboard. The PC is now with the shop where I bought it and they are running extensive tests to locate the issue.
My conclusion: Despite vendor assurances about compatibility etc., my hardware is still pretty much bleeding edge and may cause unpleasant surprises (like instability, boot failures, corrupted files and file systems, etc.). For reference, I tried to install Windows 7 64 bit Ultimate which ran the installer fine but quit at the first reboot.
My advise with this kind of hardware (see my signature below) is this:
1. Don't even think about installing your OS right away! Download and run some stress test software for a couple of days, including RAM tests. In my case, the RAM test would sometimes pass without issues, but sometimes show random errors.
2. Make sure everything is installed properly, in particular the CPU and the heat sink/fans. Insufficient cooling can fry your hardware/CPU during the stress test!!! Also check that the fans are connected to the right headers! Someone reported that he connected the CPU fan to a diagnostic header on an Asus Rampage Extreme board which has a diagnostic header next to the fan headers and that diag. header was marked "CPU fan" (the marking referred to the headers on the left, not the diag header above the marking).
2. Before running any test, check your BIOS configuration! By default, the Asus Sabertooth X79 disables XMP. However, XMP must be enabled for my DDR3-1600 memory sticks to work properly. The more memory sticks you have, the more likely it is that you have to adjust voltages like VCCSA to work with the memory. Search the Internet for your RAM sticks and BIOS settings. ONLY CHANGE THE VOLTAGES ETC. WHEN THERE IS A REASON TO DO SO (e.g. memory errors or boot freezes), or when the RAM / MB manufacturer clearly advises to do so. Increasing voltages means more power consumption and increased temperatures.
3. Different motherboard BIOS releases play differently - the latest release may not always be the most stable for your system. Again, such information can be found on the Internet (I found some good advise on Tomshardware).
4. If you run into RAM errors, you may need to run the stress test plus memory test on each single DIMM module individually to isolate a bad stick (in my case with 8 sticks it takes a long time).
5. Once you can rule out any motherboard / RAM / CPU / power supply / cooling issues that should show up during a stress test / memory test over several days, go ahead with the installation.
6. Sometimes the SSD itself or the attachment of HD / SSD to the SATA connectors can make the difference between successful OS boot and failure. Some suggest to use the 6th SATA 3GB header to connect the DVD, and the SATA 6GB header for the SSD or HD, but again in some cases only the 1st SATA 3GB header would work for the SSD or HD. Go figure.
7. Modern motherboards have several SATA controllers (Intel, Marvell, etc.). Start with the Intel SATA ports for the boot disk / SSD, unless you found evidence that the others may work as well or better with your boot disk. In my case Asus denotes the Marvell SATA connectors as "data disks" and discourages their use for boot disks.
I think it wasn't a good idea to buy 8x4GB RAM sticks. Sure its nice to have 32GB memory and I do have some use for it, but the trouble of testing it and making it work can be counterproductive.
With these boards and processors, memory settings can be very finicky. In general it is suggested to run the memory at its advertised clock speed, so my DDR3-1600 should run on 1600MHz, not at the motherboard default of 1333MHz. XMP enabled should make sure it runs as advertised, BUT your milage may vary.
Moreover, a fully populated memory bank often requires fine-tuning to ensure sufficient power supply to the modules during boot and later during operation (yes, there are specific BIOS settings for the boot phase). Stick with manufacturer and XMP settings unless advised otherwise by competent people who have used the same motherboard AND exactly the same RAM kits.
Mixing different RAM modules, or even the same RAM modules from two kits, is strongly discouraged. RAM kits are matched and supposedly tested to work together. I've bought one 32GB RAM kit and it's enough trouble to get this work. There are plenty of reports from people who have tried to expand their RAM by adding another kit of the same brand and specs (for example two kits of 4x4GB). Some or lucky, but it seems many aren't.
Just because a motherboard comes with 8 DIMM slots and their specs say that 64GB are supported doesn't mean much. In retrospect, I would now have bought a 4x4GB kit giving me 16GB, and wait a year or two until there is enough real-life evidence that higher memory configurations actually work out of the box.
Sorry for taking the thread totally off-topic, but I've done serious injustice to the Linux distributions I tried when in fact all my problems originated in hardware issues.
Asus Sabertooth X79 (NOT recommended), i7 3930K CPU, 8x4GB Kingston DDR3 RAM, Noctua NH-D14 CPU cooler, Sapphire 7770 GPU, PNY Quatro 2000 GPU, Asus Xonar Essence STX, Sandisk Extreme 120GB SSD + various HD, Corsair 500R case, SeaSonic 660W Gold X PS