I've had a 45mm SKS under 8.4 and the cable used to just rub so CX9 might be ok. If you can avoid mini V please do, the pads have to sit REALLY close to the rim, no leeway for wheel to be slightly out of true and the lever pull is massive due to mechanical advantage that means they are worse with wider rims. Stay canti or go full V with travel agent.
I thought the cable pull/clearance issue might be a bit better with new-gen shimano levers which I believe have a greater cable pull. Which levers were you using?
Bike currently doesn't have any bosses, so centrepulls could be an option too, but they sound like a bit of a pain to keep well set up.
I have used the new gen shimano (5800, although 4700 has a different ratio) as well as sram (rival 1) .. I got away with it because I was using a narrow rim. Do you hate cantis?
I've had a 45mm SKS under 8.4 and the cable used to just rub so CX9 might be ok. If you can avoid mini V please do, the pads have to sit REALLY close to the rim, no leeway for wheel to be slightly out of true and the lever pull is massive due to mechanical advantage that means they are worse with wider rims. Stay canti or go full V with travel agent.