can you comment on the max speeds (say for plain serial) you can get out of the resistor and diode circuit.
It depends on the distance. You should be able to find some data on distance vs data rate for serial comms using standard RS-232 interfaces, it probably won’t be much different.
Leon
It’s also worth noting that 74HCT logic can be used to shift 3.3v outputs for 5v inputs, where 3.3v won’t make logic 1 on the 5v chip - as 3.3v meets TTL thresholds for logic 1. Also, if you have lots of lines to shift (say, from a 5v microprocessor bus to a 3.3v device) 74LVX ICs are 3.3v with 5v tolerant inputs, and are easy to get hold of - so they work well as level shifters.