Im facing the same issues as you do Gabriel. I also have the 27" mac, although not with thunderbolt, so my options for resolve on the iMac are zero. I'm gonna build a pc dedicated to work with Resolve and for for referencing I'm lookin into different monitors from around 4 to 5k. I'm expecting the whole setup to be around 7k.
I think the only solution, without buying a new computer, is one of Blackmagics' thunderbolt products like the 'intensity'. That way you can at least see the actual signal you're producing.
But... You might wanna wait a little and see what goes on at NAB this year, cause I'm expecting Adobe to release Speedgrade very soon. The previous, or current version of this software runs very well on the iMac, in my experience even a lot faster. I don't know how they handle their signal output, but it's worth a google.
good luck
Avid/FCP Editor, Amsterdam, The Netherlands
http://www.pepijnklijs.nl
