I know this is an older thread, but I wanted to add some additional information and experience. I have a Vivaldi stack including the Clock in my speaker system. I added a Cybershaft OP21A to the stack, and I enjoy the sound quality. I am about to try an SRS Perf10, and here is why. There are apparently many different approaches to clocking. dCS employs a lower bandwidth, slower PLL approach in the Vivaldi Master Clock. This makes it efective at filtering out the generally larger amounts of short term jitter in an atomic clock, while gaining the benefits of its long-term stability. This is just me paraphrasing what dCS engineers share on their community forum. What I am learning is that there is no one best clock for every other reference and/or master clock. One needs to understand what the baseline approach is, and it's not necessarily all about the specs.
On a spec sheet, the OCXO Cybershaft appears more accurate, with lower phase noise, than the Vivaldi Master Clock, and so it should provide some benefit. In my system, it certainly sounds like an improvement, though it is more subtle than the addition of the Vivaldi Clock itself. Theoretically, though, the better long-term accuracy of the SRS Perf10 should provide an even greater benefit, especially since it has been built to also have excellent short term stability (i.e., not add any more short-term jitter that the Vivaldi Clock and DAC are required to filter out). SRS make their own rubidium oscillators, the same used by Esoteric in the Grandioso G1, I believe. We'll see how it goes. I am also trying to arrange loan of an Antelope 10MX to see whether it has any discernibly different SQ effect.
