I was about a week into my m-c hg-git conversion* when gps blogged about faster hg-git.
I was about two weeks into the initial conversion when I tried the latest upstream hg-git, with gps' patches. That conversion finished in less than a day, while the initial conversion was still chugging along on a different core. However, the git shas differed from our existing pre-cvs conversion repositories. This was due to different behavior when faced with a bogus email address.
Once I backed out the corresponding email munging commits, and landed Ehsan's timezone fix for a separate issue that halted the conversion process, we're now back to a converted m-c with the same shas.
At this point I killed the still-running initial conversion.
I'm still working on automating the cvs prepending and pulling in other repos/branches, but this is a good sanity-check point.
* Note, I had pulled both mozilla-central and mozilla-b2g18 into the same working directory as a proof-of-concept workflow test before converting. In hindsight this was a terrible decision, as it more than doubled the estimated conversion time.