Mine starts freezing over Greenland, too!
Flying KJFK-VHHH, she hums along nicely until somewhere over Greenland, then I see repeated freezes lasting 5 to 15 minutes, but if I let it go it eventually seems to somehow settle down after heading south over Asia and then I don't see any more freezes until the end of the flight. I've been wondering whether the length of the flights I've been attempting has something to do with this. It only seems to start when I'm a good 5 or 6 hours into a 15+ hour flight.
I've tried disabling all my extras, including FSUIPC autosave, Opus weather and UT2, but still get the freezes.
Another thing I tried was to delete my Logbook.bin file. I found some old forum messages indicating that it could be a source of freezes. That hasn't cured the problem, either, although at first it seemed that I was getting the freezes less frequently.
Frustrating.