I shoot the 300 mag in a 26 inch, Encore factory blue barrel and in a Ruger #1 Stainless with a 26 inch barrel. I shoot .270 in a 22 inch Remington BDL blued barrel, a 24 inch stainless barrel Remington BDL and a 26 inch Heavy barreled Remington Sendero. I shoot the 7 mag in a 24 inch blue, Remington BDL. I reload for all of them. This is what I have observed from my Chrony.
First, there is a major difference in the perceived recoil between the Encore and the Ruger #1. I alway creep up on the stock of any gun and the Encore (being lighter) has bitten me between the eyes so many times you would think I would learn. This summer it gets a 6 X 42 Leupold with 4+ inches of eye relief.
Second, the 300 mag is a definate step up from the 7 mag and the .270. using heavier bullets. I use only 180 gr bullets in the 300 mag and it is a bit over kill on white tails in KY and SC.
Third, If you reload using slow burning powders, and push the .270 to the max there is a 150 to 200 feet per second difference in my 22 inch barrel and my 26 inch barreled guns. In a 26 inch barrel the .270 (with the right loads) starts bumping into the 7 mag factory loads in a 24 inch factory barrel. The .270 has show me more variance in velocity per inch of barrel than any caliber I have used (I haven't missed many).
Fourth, I consider all three caliber more than adaquate for any deer in North America, assuming you put the right bullet in the right place.
Fifth, Hearing, I always wear hearing protection at the bench and never when hunting. I can't ever remember hearing myself shoot when hunting. I do not recommend this for any one and make my grand kids use hearing protection when possible when they hunt with me.
Sixth, Remington bullets have alway done a nice job for me, but recognize that there maybe better choices if your rifle doesn't shoot these well.