Alex@ro shares his findings tuning the RTL/IO timings on ASUS ROG Maximus VIII motherboards in a thread posted on the forums.
In a a picture-heavy thread, Alex@ro from Romania helps you to get somehow near the SuperPI 32M efficiency of Bullant. Althought I personally won't be able to get close to Bullant, the more experience extreme Skylake overclockers might. The trick with RTL/IO tuning is in memory training. In particular, the IO Latency Offset and the IO Latency RFR Delay are of importance. To start of the process, start at DDR4-3000 C11 and configure the RTL Initial Value to the lowest it can boot.
Then, increase the IO Latency Offset by one integer. After a reboot you will find the RTL/IO values to have tightened up, resulting in higher performance. Repeat this process until you fail to POST the system. In the examples Alex@ro presents in the forum, you can see a gain from DDR4-3600 RTL/IO (auto) 53/50/11/6 to an optimized 49/50/5/4.
For more information, check out the forum thread HERE.