I have dozens of elk under my belt, and hunt each year to fill my freezer, as I don't buy store bought meat other than bacon. A few things first. The style of hunting you do, and terrain you will be hunting is pretty important. Elk have a tendency to not stick around once they determine there is danger and they will be into the timber, or over a ridge in no time. They can run at an impressive speed, and once they are running at full speed, unless you are very close, and you are experienced at shooting at running game, you don't really have any business shooting at them.
It would help to know what type of rifle you are shooting.
I have two main rifles that I kill elk with regularly. One is a 20" .308 T3, and the other is a 24" .300 wm T3. The .308 sports an NF 2.5-10x24, and the .300 has a fixed 10X MIL/MIL SWFA.
This cow was taken at 400-450? something (cant recall, it was 3 years ago) with my .300
This cow was taken with my .308 at 615 yards with a 155 Scenar.
With that out of the way, this is another important part. Elk can and do range in size substantially, so attempting to get your range estimation using the animal is a very bad idea. Mature bulls and cows can vary by literally hundreds of pounds.
Elk hunting is not ringing steel, and you need a laser rangefinder. Elk will move without warning.
Binoculars and a rangefinder are FAR more important than a huge scope. I always try to limit my shots to a certain distance, based on environmentals and capability.
Often you will be cold and tired and you will not be performing at your best. More often than not, in fact.
While I have shot a number of elk with my Sako TRG, I still used my
binos and LRF to locate and range them.
As far as a scope goes, if I were in the market today for an all around optic, I would take a hard look at the SWFA 3-15 MIL/MIL. That has plenty of power on the high end, and still can be left on a reasonably lower setting such as 5X for acquiring the animal in a hurry. Plus it has an very usable reticle.
My oldest daughter's first elk was about 5 years ago and she punched it at 375 yards with a single 155 Scenar right behind the shoulder, where I instructed her to. A different scope was used, but it was set at 6X.
In reference to the illuminated reticle, It is very rare the times that you may need one. States have certain regulations in regards to legal shooting hours that must be adhered to, as well as some (not all) states do not allow illuminated reticles. Check your intended state's regulations. Generally speaking if it is so dark that I can't see the reticle in my scope, it is not a good idea to be shooting. Not always the case, but I have never needed to turn on the reticle in my NF when hunting.