25-30 sounds close but I wont know until I try it out.
Discounting whatever I put over my legs,
If you run the CLO calc for 2.5+5 just for the upppr body you end up with about 10dF. The IX should add another 10dF but its opened up a lot.
I used the single layer IX alone in just a M50 shell and I got down barely to 65dF sleeping with nothing on.
With thinner legs you would give up some warmth so 30 would be a good guess, IE the IX layer, jacket, elephants foot would boost it 20-25dF.