I order my meaties from Welp. I have ordered from McMurry for the past 2 years in a row, but this year switched. Our fair judge last summer made the comment that Welp's cornish x's are superior to most other hatcheries birds that he sees , and that is the only place he uses to order his birds from. So, we gave them a try. So far they are only 3 1/2 weeks old, and are doing great. They are already more lively than the batches we got from McMurray. We ordered 25, got 26, and lost one at day 3. They are out on pasture now and we strictly adhear to Welp's feeding directions. They have a growth chart for their meaties that you can check out here:
http://www.welphatchery.com/cornish_rock_care.asp
Can't wait to see how these guys stand up to the competition at fair this year.
Opps. To answer some of your other questions, we have our 25 birds in a 6'x12' tractor that we move twice a day, possibly more as they get larger. That is certainly plenty of space for 25 birds. We just move the tractor down the yard, turn to the next lane and move it back down the yard again. Bonus of nice lawn fetilizer too! Also, ours are going through about 3 lbs of 22% ration a day. We will only have our birds for about 6-7 weeks, and then we will butcher. We prefer our birds to be "broilers" and not "roasters", the difference being the former are less than 5 1/2 pounds and the latter, more. So if you went with cornish x's you would most certainly be done in less than 4 months.
I think many people say that cornish x's are "creepy" because they are more similar to little pigs than chickens. They are breed to gain weight quickly. That means they eat and poop A LOT. For the time invested though, their is no dual purpose that will come anywhere close, either in growth or amount of meat.
Good luck with your choice!