Back when it launched, it was quite obvious that we will see some quite high frequency records from DDR4 memory and the new G.Skill record of 4255MHz is definitely a great result, especially considering that it was done on a 4GB module with 18-18-18-64 latencies.
The G.Skill DDR4 module was pushed to 4255MHz on the Asus Rampage V Extreme motherboard paired up with Intel's Core i7-5960X processor.
The entire setup was heavily cooled down to sub-zero temperatures with LN2 and G.Skill was quite happy to supply the CPU-Z validation page link.