Apologies for the late reply. I thought I replied earlier.
For stability and performance, try to keep QPI link between 6400MT/s and 8000MT/s. I doubt the higher settings you posted will work. The highest I can get stable is 8000MT/s. Above that it won't post without increasing PCIe, but that causes USB, Sata, and anything in the PCIe slots to become unstable.
For RAM you want the best ratio between clocks/timings, but higher clocks tends to be better. If you just need to loosen CAS to get more clocks, then do that. CAS doesn't affect performance as much as the rest of the timings. Lowering Activate to Activate delay (tRRD), and Four Activate Window (tFAW), can drastically affect performance if your motherboard is setting those too high. Setting tFAW to 4 x tRRD or lower basically disables tFAW. tRRD will default to 4 if set lower than 4. These settings will vary between memory manufacturers and revisions. I'm familiar with Samsung 2gb rev C and rev D chips. They can run tRRD at 4 up to at least 2200Mhz. The rev C tend to require +1 primary timings compared to rev D. For example:
Rev C: 2133Mhz 10-11-11-27 1.5V
Rev D: 2133Mhz 9-10-10-24 1.5V
6x sticks was difficult to stabilize above 2000Mhz. I think its temperature related. I can pass any stress test, but loading up a game causes it to throw WHEA errors, and occasionally blue screen. Higher voltage worsened stability. 3x sticks I was able to get to about 2400Mhz, but I wouldn't call it 100% stable since I didn't do long term stress tests.
Others like Elpida, Hynix Micron, etc I'm not familiar with. I have some experience with Micron 4gb chips found on 8GB Crucial Ballistix Tactical LP . Those tend to do 2000Mhz 9-9-9-27, but they require higher tRFC, 160 or higher. I haven't fine tuned the secondary timings.
