You have room to increase vcore, so you should be able to get a bit more out of the CPU. You may just need to start using a mem divider if you RAM is capping at 260.
I probably wouldn't loosen timings any more than they are, so that would mean the only way to get higher RAM speed would to be increasing vdimm, but if it really doesn't like more than 2.6 vdimm (which seems odd), just put a divider on it and try to pump a little more out of the CPU.