What the ratings mean in practice
IP65 on a panel-mount unit applies to the front face once the unit is installed with its gasket against the enclosure. The back of the panel lives inside the cabinet, which is assumed to be dry. That assumption holds for most machines and fails in three common situations: washdown rooms, outdoor cabinets with condensation, and pits.
IP67 over the whole unit applies to the panel as a sealed object. It can be hosed, it can be splashed from any direction, and the mainboard is protected even if the cabinet door is open.
How a sealed panel is built
The difference is not a thicker gasket. A sealed panel uses blind-hole clips so there is no through-path into the mainboard, a breathable valve that equalises pressure while blocking water vapour, corrosion-resistant screws and connectors behind silicone-gasket covers. Those are design decisions, and they are why the sealed models are a separate product rather than an option code.
Choosing
Ask one question: will water be directed at the panel, or will the cabinet be wet inside? If yes to either, specify the sealed panel. If the panel lives behind a closed door in a dry room, IP65 front is correct and the sealed unit is money spent on a problem the machine does not have.
One caveat: a sealed panel still needs the enclosure to drain. Water that pools behind the door will find the cable glands before it finds the panel.
Condensation is the harder problem
In an outdoor cabinet, temperature cycling pulls moisture through the gland and condenses it on the coldest surface — usually the inside of the panel. The breathable valve on the sealed models helps by equalising pressure without letting liquid through, but the cabinet still needs a heater or a breather. A panel rated IP67 in a cabinet full of condensation is a warranty claim waiting for a winter.