Also, it’s not velocity that wears a barrel faster. It’s max charges in general. All else being equal, a max charge of a heavier slower bullet will cause more wear than a max charge of a lighter faster bullet. A heavier bullet has more inertia and takes longer to make the initial jump, causing the intense heat and pressure to occur near the throat longer. Longer heavier bullets also have a larger bearing surface typically.
A barrel has a lifespan of say 2 seconds. But drawn out over thousands of shots. So the longer each shot takes to get down the tube, the shorter the lifespan (All else being equal)
There are SO many variables, pretty much the more overbore a case is for a given caliber, the more wear it will cause. The two rounds are pretty equal in life with the 6mm being marginally shorter assuming all else equal. But we are splitting hairs here.