I have both right now RIR and Orps. The Buff Orpingtons I have never raised until this year. I have 25 in a chicken tractor that were ordered to fill the freezer and are due to be processed in Mid November. We ordered these just for the dual purpose reason to see how they actually would be beneficial to the farm. I also order Cornish X broilers in the spring and fall. The Orps and Cornish X will all be ready at the same time to compare the results of their weight and overall care. You honestly can't beat the fast growth of the Corish X's. I will post my results in the meat section at that time. The RIR I keep mainly for egg production, I have not processed any for meat at this time but will in the future.
I have some buff orpingtons I hatched from a seller here on BYC and some Buckeyes (purchased some chicks and hatched some eggs) that I also got on byc. The orpingtons have not filled out near as well as the buckeyes. I will probably keep them around to see about egg production, but for a general dual purpose, I was greatly disappointed in the amount of meat on the carcass. I haven't had RIR, so I can't comment on that.
DH and I just processed 18 BO roos. They were about 22wks old. Although they were tall birds and looked filled out, I was really surprised how small they were. We decided, that for as much as they ate, we would try cornish X's next time. Now, we haven't tasted them yet. The meat is very red. Almost like wild pheasant or rabbit. Feed? Free range? We're anxious to see how they taste. I'm not quite ready to fix chicken yet.
I just got them into the freezer. Because they are so small, I'm going to can them later.