I would highly recommend not to use a micro faster than needed! It's not only the clock frequency what counts, but also the edges. In order to prepare a micro for high clock frequencies manufacturer makes the edges much more steep. This can result in tremendeous trouble, because the edges stay such steep even if clock frequency is lowered.

As Rob already mentioned, for a micro that is that fast as the one you choosed, a four layer design is a must. And as Erik had already stated earlier, creating layout by using four layer board can lead much faster to a solution and become much simpler.



74HCT series is designed to have +4.5V...+5.5V supply voltage only!

Kai