We have had day old's from Poulet Anglais too. Very good service. The chickens grew at a rate of knots, they say ready to slaughter at 8-10 weeks, which will give an oven ready weight of about 3 lb or more, but we left them a couple more weeks and got some good sized birds. We killed the cockerals first as thet were the biggest.
We have a few left to kill and wont be getting any more now till spring. The chicks have to be kept under heat and as we reared them when the weather was hot we only had them under for about 3 weeks, but this time of yr they would need heat for much longer. Economically it's not the best idea.
We had the Hubbards, 'JA57' type. A white bird specifically bred for the table. They look quite different from a laying hen, much thicker legs and obviously more 'meaty'. They sit down a lot which is strange after seeing hens on their feet and active all day. It is due to their weight I suppose.
We found them to be hardy and healthy birds and have had no problems with them. We feed them growers pellets, (chicken rearer/finisher). They have to kept seperate from the hens as they have different food so we had to fence off a new area and get another shed.
Good luck if you do decide to do it, but remember there is a lot of work involved with killing, plucking and gutting, it's not a 2 minute job. The meat is denser and tastier than flabby supermarket chicken and does benefit from slower cooking.