Hi @gavinhans
Nexus 5600/6000 are having a generation 3 of ASIC on them (called Bigsur), while Nexus 5500 are having generation 2 ASICs (called Carmel). Below are some charts showing the platforms evolution and a comparison between h/w capabilities:
Pictures are taken from: BRKARC-3452 / 2015.
Of course, hardware capabilities are not the only difference. Nexus 5600 support a wider varieties of protocols which are not supported by Nexus 5500 (example VXLAN). For further details of supported features you will need to check the release notes.
Stay safe,
Sergiu
