The upper is more pliable with fewer thick overlays or Endofit bootie so there is more room all around than in other Salomon. Jeff: Sam gives a great overall description above and touches upon many of the points I wanted to cover.

Most runners and hikers appreciate having enough room for the toes to splay, but this may not be ideal for those who have to ascend and descend while hiking or running on the trail as this requires a snugger fit. These were just enough to handle everything short of what might require a waterproof shoe or something with additional traction. The Salomon Supercross 3 GTX has the advantage of an OrthoLite Sockliner designed solely for comfort.The upper of this shoe is made of durable rip-stop mesh that is relatively hot and not the most breathable. I’ll be using the Supercross for casual runs/hikes for sure, but I think it will also morph into an everyday shoe for me as the temps cool and especially as the snow flies, as the aggressive tread will be welcome on snowy days trying to not slip walking the dog or running errands. However, I would be wary of using these too confidently for any technical mountain walks or for dangerous descent where lacking ultimate traction and stability could result in injury.

The Supercross fixes that issue with a wider design, while also employing a carriage system in the upper that is a bit looser and less tight.

Fit on both is generous as Salomon go with the X clearly more locked down and the Super more open and easy in fit. The Salomon S/LAB Ultra 3 trail running shoe provides a comfort level so high you'll think you're wearing a road running shoe. My long Ultras are done for the year, and my mileage has tapered off a bit, but the trails around Missoula are still pretty run-able. The wider forefoot platform makes landing and taking off easier than the narrower Speedcross, but on sidehills and when going steeply downhill, the high heel doesn't really do one any favors. The Speedcross leans far more on extreme grip with its yet more prominent lugs and deeply bowed and arched underfoot profile and thus use in snow and mud while the Supercross is clearly leans more towards versatility on more varied terrain.