drywall on cathedral ceiling


I have a cathedral ceiling in my living room. I've installed rigid foam boards in between the rafters which are 2x6's spaced 16" OC. I've been reading a lot about how to attach the drywall over that and my question is do I need furring strips or can I attach the drywall directly to the bottom of the rafters? That would be easier and, it seems to me, stronger but I have two concerns.
Firstly I'm worried that the 2x6's will provide a path for cold to flow down from the roof in the winter and that I could end up with the rafters outlines being visible on the ceiling side of the drywall due to the temperature difference. Secondly, I read that the rigid foam expands a little and if I connect the drywall flat against it, it will eventually push out and dimple the screws.
The other idea I've read about is to thermally isolate the rafters from the drywall via a layer of thin foam board with furring strips over that. Then using long screws through the layers of drywall, furring strips, and foam into the rafters to affix the ceiling.
Is that overkill?
Thanks for any advice!
Andrew
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On Mar 1, 1:31 pm, thestuccocompany_at_coralcomputer_dot snipped-for-privacy@foo.com (mdudu) wrote:

You might want to review the material at Building Science Corporation web site. You don't say whether the rafter space is vented or not and how the board insulation is mounted or what climate your are dealing with. TB
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So he told all of em to go pound sand, sold all his stuff, liquidated everything to double eagles and moved to a studio apartment on the Cayman islands and rented a fleet of hot n cold running ho's.....and lived happily ever after.
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