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.
