??? So you bring a knife to a gun fight? ELR starts at 1500 yards and goes to 3500+ yards if you can't compete to the very end you not shooting ELR. If you cant see your splash what are you going to correct. . So to answer you question yes its worth the investment if your planning on being competitive if not your just wasting money on a hope and prayer to try to connect on steel .
I would have to disagree with the statement that Extreme Long Range starts at 1500 yards these days.
I'd suggest that 1500 yards to 1 mile is mid-range long distance and actual ELR currently is something that really is in the 2500 yards and beyond range. The ones in serious ELR circles are pushing 3000 and 4000 yards with a mile and 2500 as like the first stops to making sure you have your wind calls correct.
The Op mentioned he had a place to shoot up to a mile.
The Op also mentioned his current experience is with 6.5cm
Telling someone that only has range to shoot to a mile and doesn't seem to even have any magnum experience to jump into the deep end of the pool, seems like something that would be setting them up for failure.
Assuming 1 mile is all they have range to shoot, I think they would be much better served by a simpler system in the .300NM (or .338LM if they prefer) that can easily handle that distance while not being too expensive or too exotic. You can grab good target factory ammunition for the .300NM in a pinch that would let you get to a mile and loading for it is cheap and easy compared to the bigger stuff.
Sure, you can jump into the deep end with the .375, .408, .416 .50 caliber types in the 50 pound gun class for shooting to a mile.
But you might have more fun at a mile and get more shooting done with a much more standard setup in the above suggested calibers.
Then once you get good at shooting to a mile and find a place to shoot out much further then get something bigger.
I'd suggest even in that case, they might find themselves still putting a lot of use on their smaller stuff as well.