Honestly, there's a reason that the crown for best meat bird is a fight between strains of Cx, and that most "dual purpose" lines have become primary egg layers, and that reason is math. Cx get a lot of things very right, at the expense of virtually everything else - and then are produced at...
I'm not saying don't try - I've already linked the thread documenting my own efforts. I **AM** saying, moderate your expectations and extend your time scale. Even the Color Broilers and the various Ranger line are the products of decades efforts - efforts which don't satisfy you.
A quick, self breeding, meat bird that tolerate "ranging" is basically the Holy Grail right now.
I'll grant a lot of historically "dual purpose" birds have been bred to focus on egg production for decades, and that some real improvements can be made breeding meat back onto those bones - but...
So are we all.
The only thing that competes with a CX is another strain of CX. If a distant second will do, you have options - but none will be CX-like. Recommend you not start your project as I did, but start instead with Rangers, Color Broilers, or similar, then cull hard, saving only the...