Paul:
I'm 5'8", 173lb, 36" waist.
My large Houdini (new version, year old) over thin shirt and medium weight fleece fits with space to spare but not a lot. It's OK with thin shirt and 2 medium weight fleeces, but no spare room. It fits comfortably over a pata. nanopuff pullover.
My medium Camp magic anorak fits over thin shirt plus medium fleece, but is little tight. I've worn it over two thinner powerstretch fleeces and it fits but is bit tight; the problem with that arrangement is that since it's not full zip it gets too warm and you have to take it off. It fits over the nanopuff but is tight. I'd guess we'll both be OK with the Large but perhaps XL if you're using more layers underneath. Camp's customer service was helpful in advising on size.
In terms of breathability, the Camp magic is windproof but breathable and the new Houdini is windproof but not breathable. The Camp magic is definitely more breathable than the newer Houdinis.