Cat 5 vs Cat 5e Cabling – Physical Differences

There's no telecommunication difference (e.g. noise, crimping, termination), just the sheathing. The difference is an electrical code safety issue.

Regular network cable (i.e. non-plenum) is flammable, can catch fire, can spread fire, and emit toxic fumes when burning.

Plenum quality cable is required for use if you run your cable in air handling spaces (i.e. air ducts), or if you're running them between floors. Plenum cable is fire-resistant (it will melt, but not support combustion or carry a flame). It also emits less toxic fumes when it does burn.

If you look at some network cable, you can see which type it is:

• CMP: Plenum rated cable (plenum means "air handling space")
• CMR: Riser rated cable (riser means "between floors")
• LSZH: Low smoke zero halogen rated cable
• CM/CMG/CMx: General purpose cable
• PVC: Unrated cable

CMP burning:

CMR burning:

Notes

• CAT6 is still very precise about how the cables are terminated. Sloppy termination will reduce the capacity of the run. This is generally not the case with CAT5.

• The linked wikipedia article, has good diagrams illustrating what is plenum space and what isn't. Generally, you should use plenum cable in a dropped ceiling unless you are certain that it is not air-handling space. If a duct in your drop ceiling is missing a section: your drop ceiling suddenly, inadvertently, becomes an air-handling space.

See also

• Wikipedia: Plenum cable
• Videos of different types of network cables burning

"It depends". To the best of my knowledge, the standards themselves do not mandate any changes to the plugs. I would guess -- but I'm not 100% sure -- that the standards are mainly concerned with externally observable characteristics of the cabling such as crosstalk and attenuation, and leave the internal implementation details mostly up to each manufacturer. Having said that, the following comes to mind:

• 23 gauge copper wiring (thicker wires) is more common in Cat6 installations than in Cat5 in my experience. If the wires are thicker, the plugs are different.
• More and more manufacturers are updating their cabling systems, both to allow faster cabling work, and to ensure more consistent and/or higher quality. Many cabling systems now use a little 'form' to hold the wires in place before the plug. This is to minimize crosstalk and noise near the plug (where the cable is un-twisted, and much more susceptible to interference).
• See John Gardeniers answer regarding stranded / solid wiring; these should use different plugs. Solid wiring is often used in building wiring.

Regarding OP's link to a no-name plug, I think it's mostly marketing. While there can and should be differences in how plugs are designed, in the no-name space I don't think you'll find a consistent set of differences between no-name Cat5 and Cat6 plugs.

Here is a little video that shows how some modern structured cabling systems use an insert / form. The same brand uses a "smart connector" for the 8P8C plugs as well. But this is a name-brand structured cabling system. Cabling systems will typically be installed by certified installators, and be validated end-to-end after installation by measuring that they meet or exceed an agreed level of performance.