Adam,
Better question is what can a 7mm do that YOU can't do with a .280? Can YOU shoot well enough to take advantage of the slightly flatter trajectory? Will that additional energy/velocity matter at 350+ yards? I'd say no, not at 350. Is that 7 or so inches of flatter trajectory at 500 yards going to matter? I've killed elk with a .280 and it does just fine, but I also trust physics. A 7mm is more powerful and delivers more energy downrange. But, so what? Is it enough to matter? In my opinion, no, not at the ranges most elk are shot at.
Since I can't see a question in your statement, I'm assuming you're asking if your .280 is enough for elk. It certainly is. But if you already have a 7mm Rem Mag, I would consider taking it instead.
