Recommendations

IEEE standards do not require Class 4/Type 2 PSE to interoperate with Class 5-8 PDs. However, the PLC mutual identification in the beginning of power-up cycle will indicate to a class 5-8 PD that it is connected to PSE capable of only 30W. If required, a class 5-8 PD can power up with 30W and operate in reduced functionality modes.
Some Class 5-8 PDs may require their full requested power. The PD can power up and shut down when exceeding iCut ~33W in Class4/Type 2 switches.
Ensure that the PSE port supports the same or higher Class than the connected PD Class for interoperability.

You can continue to use Cat5e cable deployments to deliver power. Operating at link speeds of 5Gbps or greater may require you to limit the cable length to less than 100 meter. This limitation is imposed by the Ethernet physical capabilities and not by the PoE standard.