Brave? Nah - just completely nutty
I did keep an eye in the mirrors though
I've ridden quite a few 70 mph dual carriageways. On a quiet morning, the A5 around Shrewsbury, I took primary in the left hand lane. Everything moved over into lane 2 to pass.
Then the A5 near Tamworth. I rode in the hardstrip. It was as scary as hell as most drivers didn't even move over, not even to the right hand side of the left lane, and I had to cross rumble strips at each junction.
I cycled on the A34 Manchester to Wilmslow regularly for a while. I generally rode in secondary position, and some drivers (roughly 1 or 2 in every five) would still squeeze by in the left hand lane. Some surprisingly when the right hand lane was clear. This was 40 and 50 mph restricted.
If I see a cyclist on a DC I always wait until I can move fully over into the right hand lane before overtaking. It would just be cool if other cyclists would do the same.
Cyclists stand out on fast DCs as they are uncommonly sited on them. The only way they aren't seen is if drivers are not looking. IMHO