The 284 caliber provides sufficient velocity and energy to harvest deer out to ~950-1000 yds from a 7mm Rem Mag or 7mm WSM
From a 280 Rem I'd cut the maximum yardage back to ~800. 280 AI out to about ~900 yds.
Depends on your perspective of long range when it comes time to picking a specific cartridge for the .284 caliber bullets. The 7mm bullets available to us are pretty darn efficient BC wise, and if deer is the sized game you're focused on, your certainly don't need to go any larger in caliber than 284.
If you were to include brown bear, moose, and elk as typical game species, I'd suggest the .308 or .338 caliber cartridges.