It was my understanding that Meyer Lemon is about the same cold hardiness as a mandarin (as it's basically believed to have originated from citron x mandarin hybridization) and that Australian Desert Lime (C. glauca) has about as much cold hardiness as Satsuma mandarin. But who knows? It's possible that combining different cold hardiness genes from two lineages that are so different from each other may end up getting something with even more cold resistance.
I think Meyer Lemon is a little bit more vigorous growing than mandarins though, the result of its citron parentage. For although the vulnerability of citron to cold sits right between the levels of limes and common lemons--that is to say very low tolerance to cold--the inclusion of this parentage may be allowing the Meyer Lemon to bounce back more easily from any cold damage, making it more resilient. I've read numerous reports of Meyer Lemon being able to survive (albeit not the best) in zone 8a, but never heard anything about about mandarins (other than Satsuma) growing in this zone, but that may just be because Meyer Lemons are a lot more popular than mandarins, so could just be due to a lower liklihood of ordinary people having experimented with them in this marginal climate zone.
Austalian desert lime, of course, is very drought tolerant and resilient (as it had to be in its native environment).
All I can comment is that, judging just by its parentage, I don't believe Eremolemon would be appropriate in climate zone 7, unless possibly if it was set up in a warmer microclimate.
(if you're familiar with how to shape a landscape to create a microclimate, things that help give maximum exposure to sun and retain heat)
