Floyd - You're definitely right - sorry I wasn't clear on that one...I have been to Andreas' house and seen the clips he's using, so I knew he was talking about the V-clip rather than the Whisperclip. I'm pretty sure the difference between the RSIC-1 clip and the V-Clip is 1/2".
Andreas - Yeah, I just called one of the bigger local plumbing/HVAC etc. places and they said their rate is $125 for first hour, $95 each additional hour, plus you pay travel time. Annnnnd he said 3-4 hours to move the pipe. OUCH. Then add in an additional hour or more to move the refrigerator water shutoff and materials and I'm into this for $750 or more. Grrrrrrr.
Cutter - I think you're probably right, but the last thing I want is to leave the pipe, hang a ton of drywall, finish the rest of the room, and then regret a $500 mistake (relatively small in the grand scheme).
I am also thinking that once all the weight of the DD + GG is on the clips and channel on the ceiling, I might have a little flexing in the channel (I'm using 20 gauge per DE), giving me a little more distance between drywall and joist. Anyone know if this is likely to be true?
Long story short, the plan for now is as follows: get a few clips and some channel, jack that pipe up so it's super-snug against the joist, and check to see if I have clearance. If not, call a more reasonably priced plumber than the shop I was just talking to.
Here's a pic of the pipe. You can see how thick it is by comparing to the hot/cold lines on the other side of the pic. Those will fit easily between the joist and drywall. You can also see that the rigid foam is almost complete.