.223 vs .308 (Or Other)
I'm am "old guy," and it means I have lots of opinions. Fortunately, it also means I have lots of rifles! I have hunted deer in NY, VT, and MT. I also shoot target a lot, 'cause I'm a reloader in search of the "Holy Grail" for each of my rifles.
I own a S&W MP15 flattop. I started deer hunting 50 years ago, with a borrowed 6.5x55 Swede - a great cartridge, BTW. My high school graduation gift from Dad was a Remington 760 in .270, and I hunted that through my 20's and into my 30's. I no longer own the Remington 760; now I have a Ruger M77 Mk II, and it shoots 1/2 moa @100yds. It will push a 150gr. bullet at 3,000fps to do that, and it's equally good with 130gr. loads for deer.
I have owned, hunted, and liked, a pre-64 Win Model 70 in '06. I have also owned and hunted a Weatherby Vanguard in .308. My current go-to gun for deer is a Ruger 77 (early) in .257 Roberts, but this year up north in NY State where I live, there are bears all over the place (including in my driveway 2 nights ago!). I am hunting my .270 with 150gr. loads for that reason. My wife has decided to leave her .243 Ruger ultralight at home, and hunt the Savage Model 99C in .308. -Both good for deer, and suitable to take a black bear down.
Yesterday in the woods, I listened to shots on the next ridge over. The rifle was semiauto, and clearly an AR. I heard the idiot fire 9 rounds at what I presume was a deer, followed by silence, then another 5 rounds. BTW, in NY the max. magazine capacity s 10 rd., and only 6 when hunting (5+1 in chamber). IMHO the .223 is NOT a good deer cartridge - multiple shots and running animal = tough, strong-tasting venison!
I think you're on-track with the idea of a .308. I love my Rugers, but they often need a little "tweaking" of bedding to make them really accurate. I also own a Savage 11FHNS in 7mmWSM, Accutrigger, and it shoots an honest 1/2moa. As others will tell you, the Savage bolts aren't pretty, but they're real accurate. I bought the 7mm short magnum because in 20 minutes I can change the barrel and have a .300WSM.
If you will primarily be hunting Eastern half of the US for the next few years, I think the .308 is "right on" for the only centerfire rifle, although a .270 might be an equally good choice.