say is that you can do it
and, after many a summer, find out that the reason for thet little strange problem popping up so very rarely was because some little function in the chip was more speed critical than the rest. Also, the chips willingness to run faster will depend on Vcc, temperature and who knows what else.

Remember: succesful testing does not prove the abscence of bugs, it proves the abscence of known bugs

Erik