If you truly want a k9athlete, a BC is the way to go. Aussie, too, make great active pets.
Highly intelligent dogs, especially BCs, are often turned over to shelters because people don't know how to 'handle' them. In some, the herding drive is so strong, people unfamiliar with the breed will never be able to channel that drive.
Lots of German Shorthairs end up in shelters too...for the same reason...and they have SO much energy. The best thing I ever did was to pick up a couple of frisbies at Petsmart one day when Belle was about six months old. She is a "natural," and just loves it...especially when I am tossing two or three at a time.
We don't have a disc dog club around here, but the neighbor kids all show up to watch. We've taught her a few tricks to go along with the routine. The hubby decided to have her launch off of his back one day...that was the same day he discovered that the professionals on TV wear protective clothing...LOL!