Re: 12x50x56
If you are shooting at stationary targets out at distances beyond 2-300 yards it may have its place. If you are trying to shoot movers or are shooting in heavy mirage, you will probably want something that dials a bit lower.
I run a fixed 10 on my TRG, but will likely move to something that is variable with a low end around 5X. Being able to dial down like Rolex pointed out above can be huge. If you are looking at the 12-50, I would urge you to look at the 5-25 instead.
Josh