6 one way half dozen the other on the calibers above...I dont see why you cant shoot 300 yrds with an 06.

30-06 will allow you to hurl a bullet 300 yrds as well and a heavier bullet to boot.

270 is a 130gr rifle...there is virtually no other load to consider for deer.

7mm08 gets you in the 140gr class and is a great caliber for whitetail...

I do prefer my 270 though for deer hunting sight in 2in high and your holding dead on out to 250yrds.. Havent really shot out past 200 with it...Never had to....and i think you will find once you do a little scouting andsee where deer are coming into these fields you should be able to set up in a position where you arent required to make a 300yrd shot...

The gun can only do so much on a longer range shot...the rest is up to you...just buying a 270 or a 7mm08 doesnt mean you can take that 300yrd shot and its lights out...