I pastured Cornish Cross, which is the standard broiler barn chickens. They are genetically predisposed to pack on as much muscle in as short a time span as possible. By the time they're ~ 9 to 10 weeks old, they are waddling giants, and I'd definitely not characterize them as exercised. :)

That said, the difference that being able to forage green grass and insects in the short period they were out on pasture (usually 4-6 weeks, weather dependent) was so remarkable in terms of the flavour and the texture of the meat, that we're effectively ruined for eating any other non-pastured chickens. The fat was rich and velvety, the dark meat was meaty and deep in flavour; everything was just moist and juicy and delicious.

We didn't do many on a yearly basis (about 1000 +/-), and I was primarily using them for fertilizing pasture that I was grazing with our dairy herd. The fact that they were spectacular eating was just a side benefit.

If you're ever able to track one down, I'd highly recommend giving one a go.