Re: 1000+ yard deer hunting
That question is way to broad and general to be answered simply. If you wait long enough you will get a ton of different answers and opinions.
But, I would say that it would be a rifle/scope/cartridge combo that is stable, accurate, repeatable and has the horsepower to push a high BC bullet as flat as possible and retain enough velocity and energy with a properly designed bullet to make a killing shot at that yardage. Remember also that in addition to the gun you will need the best rangefinder, weather acquisition system and portable software or valid range data to go along with the gun.
There are many combos that would, could and do provide what is needed to make consistent kills on deer sized animals at 1000 yards but you must also remember that conditions at the time of the shot would dictate if the shot would even be taken or not. That 1000 yard capable combo may be limited to 300-400 yards under adverse conditions.
I personally use a 7mm AM with 200 grain bullets. Others would say a big 338 such as the 338 AM but still all of the above criteria have to be met to be a consistent 1000 yard hammer on deer sized animals.;)
Also, remember that no matter whether or not you go out and plop down the big bucks to get such a gun, you still have to have the personal skills and experience to be able to make the shot.