See
https://www.youtube.com/watch?v=Mwb67g4skGMIf you have two cards (or built-in video, in case something goes wrong), you can try to take timings from frequency 1500Mhz - will be work even faster.
This may not be on all the cards, my card works with latency rate from 1350 Mhz.
You copied the 1350 timings to the higher frequencies?
Yes. But better try to copy from 1500Mhz to all higher freq. Not all cards can operate with lower latency.
I had about 15 times to flash the BIOS, to find the right latency (until memory is beginning to work perfectly)