I also ordered a straight run of heavies from McMurray about the same time... mine are about 5 weeks old now. I also got 5 of these big white birds, although curiously, the others are catching up in size now. I am new to this whole chicken thing, though, so take it all with a grain of salt. There's what i think may be a Buff Orpington that is about the same size as some of the big whites now. I also got a different kind of white bird, but I can't tell what it is yet.
The big white ones I got look identical to the ones in your pics, very friendly, and rush right over when I open the door. They don't seem any clumsier than anyone else, though, and while they towered over everyone at first, the others seem to be catching up growth-wise. I was under the impression that CornishX would just keep getting huge...
Thanks for any input,
Danielle