advice
Ok, you asked. You're looking for one rifle to do everything, a tall and if not impossible, an impractical request. Targets 100-1000 yds and enough rifle to hunt elk as well. Seems a bit much. On top of that, an optic that will be adequate for 1000 yds will be a whole lot of scope to lug around for whitetails or bear in the Alleghenies of PA or anywhere else. You really need to consider two rifles, or more precisely, two rifles chambered for different cartridges.
Dunno what access you have to shooting ranges, but 1000 yd ranges do not grow on trees, heck, a 600 yd range is not all that common in a lot of places, north Alabama for one. But if you do indeed have such opportunity, either at known or unknown distance shooting on paper or steel, the 6.5CM has a big following. Bamaboy has a couple of rifles so chambered and they are mild shooting, exceptionally flat past 300 yds to way out there and ammo is now very common. If you intend to shoot say 50-100 rds in a day at steel or paper, the difference in the recoil of a 6.5CM v. anything bigger will be much appreciated. The 6.5CM will also suffice as a deer and hog rifle as well. As I am a hunter first, taking deer typically under 100 yds, I do not need the range or the trajectory that the 6.5CM offers so do not own one myself.
The fly in the ointment is ....elk, and to some limited extent, big black bears. I will likely never get to hunt elk, but I know that an elk is not a whitetail. While a BIG whitetail runs 200 lbs +, a big bull elk can approach 800lbs, heck, maybe more. PA grows some real whopper black bears too, there are about a dozen on record, in recent years, that are in the 800 lb range. Bamasister killed one in the 500lb range, I have the skull in my den. I think a 6.5CM can surely take an elk,(or black bear) they are certainly not bulletproof, but the old adage of "use enough gun" comes to mind. I would not want to travel from the Pittsburgh area to the Rockies, to have to pass an elk on the hunt of a lifetime, or worse, LOSE an elk, due to a quartering shot wisely untaken or a bullet not getting to the vitals and escaping. unrecovered. It'd be a long drive home.
So, for my do all North America hunting rifle, I'd go with the old standby '06. A close second would be a .270 loaded with a premium bullet if elk or blackies were the quarry. Ammo everywhere, a wide selectin of bullet types, rifles in abundance, and not too much of a kicker for most folks to shoot well. Coming back to target shooting, 150 rds or so thru a SPORTER weight '06 or even a .270 over the course of a weekend, say at some type of match would be unpleasant for most of us. I've done it with an 18 lb rifle in .308, no problem, but a 8lb sporter would be painful. Hence, two rifles.
To confuse the issue, if the "light" target rifle will in reality only be shot much to 600 yds or under (most of us, way under) I would give serious thought to a .223/5.56 with a fast twist barrel to utilize heavy match bullets. Cheap to shoot, and ammo everywhere (usually). A pussycat to shoot.