Having built rifles for and owned all of the afore mentioned calibers, I was prompted to sit down last night and write a lengthy response. When it was done, I deleted it. Today, I offer a much abridged version.
SAAMI sets the Maximum Allowable Average Pressure for 270 Winchester factory ammo at 52K. The 284 Winchester ammo has a SAAMI/MAAP of 56K. It is actually standardized as a higher pressure load than the 270. The rifles Winchester chambered it in were exceptionally strong and well built: The Model 88 Lever action and the Model 100 Autoloading rifle. I still own a Model 100 and it is a strong gun that is sweet to shoot. So, pressure was never a problem for the Winchesters, nor was the 284 a "low pressure" cartridge.
In bullet weights greater than 130 grains the 284 will meet 270 speeds with many loadings, and when it can't, it comes very close; usually doing so with far less powder and pressure. As always, a greatly ignored facet of shooting and reloading is
efficiency. A smaller cartridge that can get within 5% of the maximum speeds of a larger cartridge is dismissed as a "weak sister" when in reality, it will kill the same game, just as handily as the less efficient yet larger round.
The truth of the matter is that any of the cartridges formerly mentioned, in the hands of a good rifleman, will not exhibit a dry spit's worth of difference in the field. My 2-cents worth.~Muir
PS: The 280 is far from "scuppered" and is in the views of those who have shot them, a far superior round to the 270 and far more efficient (there's that word again) than the 7mm Remington Magnum while performing in the same class. Many an elk has fallen to the 7mm Express.