Simply pinging the virtualbox cpu server gives, over a number of tests, avg
rtt around 150 µs  from both osx-x11 and osx-cocoa drawterms. (Indeed, the
latest push of osx-cocoa no longer gives the warning.)

I hope at some point it will become clear what is the matter---perhaps, as
you suggest, in my setup; although so far I don't see why the different
results I get should be due to that. Let me know if I haven't given enough
data.

And certainly the fullscreen integration of your version is nice!

Mark.