So I guess there is a difference of opinion on the speed issue. But let's set that aside for a minute.
I can use a simple resistive voltage divider (a 1K and a 2K) to knock 5V down to 3.33V. No capacitors, so I guess there is not a speed issue. But, I have a 3.3V signal coming into my ATMega1284P. Will the uC reliably read this as a logic high? If not, then maybe I need something like a TXS0102?