You are right and I am not an structural engineer, but I understand that pure strength isn't the only limiting factor for disk; they start wobbling before they tear apart (http://superuser.com/questions/554717/will-there-ever-be-fas...). That, I think, is more a matter of thickness than of pure tensile strength. Barring the construction of hollow disks, that means heavier ones.

Also, now I think a bit more about it: in a 50-speed CD player or a 16-speed DVD player, the edge of the disk moves at about half the speed of sound. Doubling rotation speed would push it over the sound barrier. I guess it would take quite a bit of research to make a CD/DVD/BlueRay player that will work fine at those speeds (a way around that is to make the disk smaller. That would be an option for a disk with the storage density discussed here, but it wouldn't win you more than a factor of four or so, at most)