Is it safe to overclock RAM above spec?

I've got 16GB of DDR4 2133 RAM that I bought last year before RAM prices surged. I've since upgraded from a i5 6500 H110 to a 7700k z270, but due to RAM prices, I stuck with the same RAM.

Yesterday I decided to see if my RAM is stable when overclocking. Using a profile in the BIOS, I overclocked the RAM to 2667mhz and everything seems stable. Benchmarks are slightly better, and the computer hasn't crashed yet. In the long term, is it safe to keep my RAM overclocked? Is it even worth the minuscule benefits? Am I shortening the life of the RAM? Thanks for the help.