Thank you very much!
Seems off-topic from this thread, but neutrinos do not travel at the speed of light because they have mass. Also check out 'neutrino decoupling' and 'cosmic neutrino background'.
The question was about neutrinos moving slow compared to light relative to comoving bodies. To even ask this question means there is no implication of any neutrino moving at c.
Further, most hits on your proposed search do not address this question, others are paywalled. However, I did finally turn up the following, which suggests at least some of flavors of relic neutrinos are non-relativistic.
Thanks again for your help.
Interesting article PAllen enjoyed reading it
However, I feel a note of caution is needed, as despite what the dark matter fraternity say; the idea that the Bullet cluster is evidence for dark matter is not unchallenged. A couple of early papers from 2010 and 2011 suggested that the in-fall velocity was too high to support dark matter. A more recent paper by Craig Lage and Glennys R. Farrar published 25 February 2015 in Journal of Cosmology and Astroparticle Physics, concluded “due to the paucity of examples of clusters with such a high mass in simulations, these features of the main cluster cannot presently be used to test ΛCDM.”
Moffat's modified gravity (MOG) addresses the Bullet Cluster without DM for example https://arxiv.org/abs/astro-ph/0702146
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