Re: 7mm Mag or 300 Mag for 1000y shots?
Check the twist it comes with in each caliber. If you want to shoot the heavy (170+ gr)high BC 7mm bullets (Berger/JLK you will need a 1-9 twist. Do not think the factory gun will come with that twist. 7mm will be limited to under 170.
Same for the 300 win, you will probably be limited to 220 and under.
Now neither option is bad, just beware of the limitations and plan for it. You are not going to shoot the heaviest, highest BC bullets for either.
JLK 7mm 168 is .690 BC
Berger 168 .648
JLK 30 cal 210 is .665
Sierra 220 MK is .629
Might want to consider a variable power scope with mil dots also. You can use 10x, but limiting closer up and sometimes you might want more power for way out.
For the money, good choices!