I too thought with the thermal bridging it would not be much better with 2x8s. Air exchangers are code for quite some time as well now here.

I think staggered 2x4s on a wide plate would be allowed although I have not seen this done for a long time locally. I have not installed triple thermopanes since we built our own house 35 years ago. If you ever have them their worth is obvious. what really surprised me back then was the reduction of noise transmission.