I'd have to disagree with that last statement....the true dual purpose breed does exist and it exists in the Plymouth White Rock, which has exceptional meat quality with a fine and dense meat fiber and huge breasts, lays on meat very well and also lays very well, with a great fertility rate, not to mention an excellent feed conversion. Before there were ever CX birds being raised commercially, there was the PWR, from whence a lot of the genetics of the CX have been borrowed. It's been said that 95% of the world's table birds have been derived from WR females.
That's one reason I marvel at all the efforts to create a dual purpose breed for meat and eggs going on all the time when the WR has been perfected for quite some time, so no need to reinvent the wheel unless one just likes to fiddle around with a hobby.
No, you won't get a bird for the table super fast like you do with the CX, but why in the world does anyone want to speed these things up all the time? The HUGE amounts fed to the CX to get them on the table is WAY more feed than one will feed to a WR in the comparative times it takes to grow each bird out, so the feed conversion isn't better, it's just quicker.