This is a bugger. Another bloody essay from maggot!!
The honest answer really is as follows I guess (in my opinion and having just splashed out for a Steiner MXi5 for a BAR10....).
CSR is short to medium range, fairly rapid at times, and it is often difficult to make out specific aiming points. You may well find that centre of mass is the best you can manage at times.
Firstly, you will be coming on aim quickly and in all lighting conditions.
* Can you pick up the ret easily against a variable background and aim accurately with it. Do you like simple or cluttered? Cross or dot?
* Can you mount the scope in such a way that that it will naturally fall on aim without moving your had about? (Airbrush once told me to stick my beak on the ARs T handle...Spot on Andy and thanks, gives you the same eye relief every time

).
The latter is important because with some scopes (and some battle scopes as it goes) because there is a compromise between mag and parallax, so a slight movement of the head can shift the MPI, particularly on lower mags. Also, all singing all dancing ranging rets might look great on the TV, but when you want to pick up a target and hit it 5 times in 20 secs while you are in the sitting position and bouncing about like a jelly....Things can get really confusing.
You will as likely be dialling elevation and possibly wind
* Do you work in MOA or MRAD?
* Are the turrets easily set and repeatable?
* If you dont dial wind and use aim off and miss drills, are there enough ref points on the central stadia (that goes through the centre when elevation is set).
It gets awful difficult to aim off for elevation and wind into the sand and why bother getting elevations if the damned sight wont track.
Do your eyes like it? Sounds daft but glass simply enhances the light entering the eye, one mans perfection may be another mans nightmare.
Look at what the military are using. I was taken with the Trigicon accufire 1-8x. I still am, but the problem to me is that it is FFP (IIRC, ret gets larger with mag) and is a cross. My eyes like dots, always have.
How much mag do you need? Many DMR rifles are fitted with 1-6x scopes for use out to 800m. Many believe that if they turn the mag down it wobbles less. Wrong. But what does happen is that you tend to chase it more and make it wobble. When you think that high power shooters shoot out to 600 with irons (accurately) then mag is a moot point in CSR as that is as far as we ever go, it may help in the urban (where the target rings are all used) or the Bisley Bullet.
Also, one of the big issues with high mag scopes is that IF you use them with a rifle that jumps about a bit (7.62x51 or even 5.56x45 with no brake, and you are not slung up) if you ignore the second principle (rifle must point naturally at the target without any undue physical effort) then when she settles after firing and you are following through, she may well settle 2 targets down (been there done it and seen it done with high mag PO rifles, it gets everyone sometime).
As has been said, do you want to shoot SO, PO or both? High mag can be a sod standing.
And finally how much are you prepared to spend? I am not rich, but knowing what I know now I wont spend less than a K on glass (unless its decent second hand). Rifles barrels burn out and peoples physiology changes, but good glass gets kept and moved to new rifles. This is not to say that lesser scopes are no good, but you will often see people trade up as they improve. There are many being used, S&B, Niteforce, Vortex, Steiner, Elcan, Trijicon,
In short the best way to find out is to go to a shoot and talk to the shooters and ideally try scopes on the rifles. I dont think there is a one size fits all people/tasks, but the number of certain Marques being used in the league by those that shoot regularly will give you an idea.