The maximum frequency of operation for the SN74HCT125DR is 40 MHz.
Yes, the SN74HCT125DR is compatible with 5V systems, but it's recommended to use a voltage regulator to ensure a stable 5V supply.
The output enable (OE) pin is active-low, meaning it should be connected to GND to enable the outputs. Leaving it unconnected or connecting it to VCC will disable the outputs.
The propagation delay of the SN74HCT125DR is approximately 10 ns.
No, the SN74HCT125DR is not compatible with 3.3V systems. It's designed to operate at 4.5V to 5.5V.