Long-Range Scope for .300 Weatherby Mag

The problem that you will run into with either brand of those scopes is not enough adjustment for Elevation.
Bushnell does have an Elite Tactical line,but I don't know how much adjustment they have,you can probably use one with a 20moa base and get the ability for 1000 yards.
I personally like the Sightron SIII scopes,and have them on my long range rifles.

The Bushnell 6500 Elite line have 80" of adjustment. That is more than any other scope I have found yet. You are looking at close to $700 for a variable power scope with the kind of power you will need.

The .300 Weatherby will have a pretty flat trajectory, and you can get a scope with a BDC reticle that will allow you got get out pretty far. However, if you want to get there using elevation adjustment, you would do well to get a tactical scope with at least a 30mm tube.
For Nikon, the only scope that really would fit the bill would be the Monarch X 4-16x50.
For Bushnell, anything in the Elite Tactical line.
I would also only recommend those scopes as you want a scope that can handle the abuse of the .300 Weatherby recoil. Most Bushnell and Nikon scopes are shockproof anyways, but you might as well get the best when dealing with a cartridge like that.