How far is a 4x?
Think of it like this:
4x will make a 400 yard target appear as if it is a 100 yard target with the naked eye.
200 yards will appear as though it is actually 50 yards with the naked eye. Divide by 4 obviously.
Now, how well can you see and place a reticle on a target at 50, 75 or 100 yards away? It is easy for you? Do you need more magnification to be able to see more detail?
I have a 4x on my AR-15. 400 yards is pretty much a max range for it as far as any kind of effectiveness is concerned (my opinion). Whatever I view at that range (400) will appear to be 100 yards away when I am looking through it. It is very easy for me to keep a reticle on a human sized target at 100 yards with no magnification. Anything under 400 yards will appear as if it is under 100 yards with the naked eye. Should be peiece of cake.
If your goal is to zero in on tiny objects, you might want more magnification. Here's a good test to determine what you NEED:
Whatever your target is -- look at it at different ranges with the naked eye until you can no longer comfortably see it or comfortably aim at it. Take that distance, and multiply it by the magnification. If that distance is 30 yards, than a 4x will give you 120 yards of range for comfortably being able to see it and targeting it. If 8x, then 240 yards, and so forth and so on. Obviously, shooting small things, like 1" or 2" paper circles at 100 yards is more difficult than aiming for and hitting a 10" circle. This is why combat optics are lower magnification, and why varmint scopes are higher magnification. In combat, low magnification is enough to do the job while still maintaining good field of view, when hunting with a rest - you don't need to be swining your rifle around, thus field of view is not very important.