I have posted on this subject a few times, but this is my opinion, FWIW:
I shoot regularly out to around 800 yards. I can make the 2-7X32 Viper work at these ranges. The 4-12 Swaro is more than adequate, and the 4-16 Viper is just about right, IMO. I used to have and use a Leupy Mark4 6.5-20 quite often, but really prefer the magnification range of the Viper.
Magnification is not needed to shoot long range. I prefer the 4-14/15/16 type scopes, but the 5/6-20/25 type scopes work well also. The problems with high mag scopes were touched on by Darin, but the biggest factor for me is FOV and mirage.
High mag scopes are pretty restricted on the top end with FOV, and target aquisition can be a bugger. The brightness thing can also be an issue, especially in the mountains, where light can be scarce during hunting hours due to terrain, IME. Sometimes mirage makes high mag scopes at high magnification unusable. One other thing, is that most 4-16ish type models have more adjustment available than their 6-24ish brothers.
If you go with a high mag scope for long range, FFP reticles are the way to go, IMO. That way you can turn down the mag for brightness or mirage issues, and still have a calibrated reticle. The reticles do get tiny at the low end though, but I have found illumination can help substantially.
On brands, there are a lot of quality scopes out there. While Leupold makes some very nice scopes, I don't prefer the VX-3 or Mark 4 series over some of their competitors, for a variety of reasons. For instance, those scopes tunnel at the lower end of the magnification range, from around 4.5 to 8 on the 4.5-14 models. This means you don't get any more FOV as you go under 8x. They also don't have a reputation for tracking perfectly. I have seen several Leupys that had a hard time returning to zero and changed adjustment click values towards the end of the adjustment range. The last Mark 4 I most recently tested, however, did not have these problems, and tracked very well. I have heard great things about the VX-6 series, especially on constant eye relief and tunneling, so they could be a great option.
I have found a lot of value in Vortex riflescopes, Sightron riflescopes, and SWFA SS riflescopes. These scopes have excellent optical performance, less tunneling, more constant eye relief, and super reliable tracking.
Nightforce scopes are the gold standard for tracking and toughness, and are good optically, but they are expensive, and there are other options at their price point.
The Euro scopes from Swarovski, Zeiss, and Leica have outstanding optical performance, and the Swaro Z3 I tested had good tracking as well, but I like ballistic reticles in these scopes.
I am glad Coyote Commander has found a system that works for him on carrying a rifle at high magnification all the time, but I personally prefer to carry my scopes at the bottom magnification, to gain the most FOV, and turn up the power for longer shots when they present themselves, and recommend this method.