If the .30-'06 can be loaded to mimic (some) .300WM performance, it should stand to reason that the .280 can deliver adequate performance to 1Kyd with a lesser flash-bang. Personally, I could make do with it and never miss the additional recoil. My paper calcs suggest a .280 with a 150gr Nosler ballistic tip should probably make it to 1000 at or near supersonic, but heavier would be more of a sure thing. A 1:9" twist should stabilize up to 168's and maybe 175's. Believe me, a 150-168gr bullet going supersonic is going to arrive with terminal performance to spare. For me, the recoil of such weights with a .300wm would be intolerable, thanks to having my sternum remodeled a couple of times.
I think that any Savage rifle chambered for .30-'06, .270, or .25-'06 can be rebarreled with a quality replacement barrel of adequate length, and the entire setup can be done a lot more simply and affordably. Or, you could simply go with a .270 sporter. The point here being that the reduced bullet cross section permits significantly improved velocity retention, allowing a lighter weight bullet to give terminal performance equivalent to a heavier bullet out of a .30.
For less distant shots, 120gr and 140gr Noslers are completely adequate in the .280, and a lot more pleasant to shoot out of a hunter weight rifle. Rem Core-Lokt 140's and Hornady 139 SST Superformance are very acceptable factory loadings for anything out to 500yd at least.
My 280's are both Ruger MKI factory rifles, one with a sporter barrel, and the other with a somewhat rarer factory varmint weight barrel. The sporter is a pleasure to carry in the field, and the varmint weight would be my choice for anything far beyond 600yd.
My thinking about extreme distance shots for big game are that as satisfying as it would be to achieve such a shot successfully, the odds for another outcome become prohibitive. Honestly, I value the cost of a wounded animal getting away to die inhumanely too high to warrant such a risk. I'm no Bambi-hugger, but I do respect the game animal too much to risk that sort of worse case scenario.
Each year, as the deer season moves along, I've seen another beautiful trophy buck dead and rotting in the deeper thickets, and that's a pretty big, bad waste in my book. I once also needed to dispatch a wounded deer that had been blinded by a faulty head shot. The animal was clearly in a state no animal deserves to be in, and the infection made the carcass too much of a gamble to harvest. The animal had clearly been in that state for days and days. So as much as our creative sides tell us it's worth doing, my experience tells me it's too big of a gamble for the animal for me to take such chances.
Greg