Another side of the coin though, is that it seems like it's a lot faster to get a male to breeding age than a female to laying age... So, you may have more luck keeping a cock alive long enough to breed him than you would with a flock of hens trying to get them to laying age.
Also, it seems like you get bigger (healthier?) chicks out of bigger eggs, so maybe a good laying breed with a hen that is already making decent sized eggs would be the better mom than a CX pullet who may be producing tiny eggs.
I agree with the first part, as I said take what you can get and run with it,
On the second part I disagree CX pullet egg is well over 2 ounces and by the 4-5th egg it is at 3 ounces. Not many layers can match them in size.