re bb7 disc flex, I adjust the non moving pad somewhat close to the disc so that not too much disc flex happens. Its easy to do and eliminates the flex issue. Learned the hard way from having too much space.

I figure both systems work well and lots of people have used bb7s now for long long trips and once you learn the tricks, they arent a problem. Im sure that spyres would be fine for me too, and I have had a mechanic tell me that they are easier to set up, but he did say also they are a bit too close to spokes....
but hey, Im sure both are fine, and again, as I have the avids, I just use em and had to learn new skills messing with them, making mistakes, not adjusting them properly, figuring it out and then living with them happily for about 4 1/2 months total of heavily loaded touring over three trips.