Here's my take on the subject..
Either way, I see the feed bill as irrelevent. If you keep a DP bird, for twice as long, but they eat half as much... does it matter if your glass is half full, or half empty? If you're planning on free ranging, most likely you'll free range with either scenario to help with feed costs.
If you want to save money, by not buying chicks every year, go DP. On the other hand, if you don't want to spend the money to maintain a trio of breeder birds for an entire year- go CX. I'd say that those two will basically cancel each other out as well.
So to sum it up:
If your after a quick turnaround, or tons of efficient meat yield- go the CX route.
If your after a enjoyment, family affair, with more "flavor" meat (or tougher, IMO), then go the DP route.
If you want a carcass comparible to a small turkey- go CX
If you want a carcass with more meat than a quail- go DP
Now, I wouldn't be an American, if I didn't do a little self promoting... Personally, for a family of two-- I feel the Cornish bantam might be the way to go, even for a family of three (eat two of them). My SQ/ BQ Cornish bantams eat very little, have monsterously positive ratios of meat to bone to size, and can self reproduce- giving you the all around good meat bird option.