Certainly some good results from the low cost crystals, Jeremy. I am encouraged, although mine will be a while turning up. I think I ordered 10 of each frequency with the intention of choosing the closest 5 for the notch filter. I recalled this morning where I saw the idea of "doubling up" the shunt crystals: it was in the July/August 2008 edition of QEX, in Wes Hayward's (W7ZOI) article on oscillator evaluation with a crystal notch filter. Looking again at that article, I see he achieved about 85 dB null depth at ~10 MHz with 5 crystals, but his crystals may have had lower ESR.
For most of my LO applications between 10 and 70 MHz I think the SML-01 in divider mode with a 20 kHz noise floor of -148 dBc will be a good enough work horse. But better sources are always good to have and are, of course, essential in more advanced applications. Wenzel's application notes are well worth reading, too, and I notice they have a number of useful schematics including a low-noise post-mixer amp for baseband work. For the 1/f and other low-frequency noise processes nothing beats some measurements, as both you and HH75 note.
I'm professionally acquainted with the team here in Perth who designed the Poseidon Scientific Instruments (now Raytheon) ultra low noise sources although I don't see myself getting hold of a sapphire resonator any time soon. But they were/are the ultimate in terms of close-in phase noise and, being 10 or 20 dB better than the Wenzel competitors in radar applications, allowed you to know that your seconds were numbered as the Patriot (or whatever) missile approached!
73, Peter.