My original Aussie, Heidi, was my running companion for years, and would go with me snowshoeing in the winter. Super smart, high energy, 85 lbs of muscle (that's big for an Aussie). Rangers at our local park were okay with me taking her off lead to do command work, could see that she was well trained (I always put her on lead when we were near people or other dogs, didn't want to abuse the privilege).
Sidney was ready for early retirement, a sweetheart.
Bear is high energy, but will run around the yard by himself if Maggie doesn't want to play.
Maggie is nowhere near Bear's size or energy level, but when she's in a playful mood she and Bear raise cain chasing each other [emoji3]
Our backyard is about 40' x 80', 5' fence, wooded outside the fenced area. I tacked on a 40 x 40 fenced garden area behind it - when the back gate is open, into the garden, they have a large play area.