From what I have learned the .270 has a flatter trajectory and if you are out in the open and trying to take game at long distance it will be more accurate. It may not be as nessacery in South Carolina compared to being out in the open spaces out west.
The advantage of the 270 is its speed and flat trajectory. It is essentially a 30-06 necked down to shoot a smaller, lighter bullet thereby achieving higher velocity. It is a popular cartridge out here in the west where 300+ yard shots are not uncommon. It is perfectly suited for deer and antelope, and will take down elk and bigger animals just fine with a well placed shot. Ammo is also widely available and inexpensive making it a good choice for any survivalist. Having said that, if you don't plan on shooting beyond 300 yards then the 270 offers no real advantages over the even more common and widely available 308 or 30-06. Personally, I shoot a 7mm Rem. Mag. and have been very pleased with its effective range and power, but the recoil is more severe, and ammo is 30-40% more expensive than comparable loads in 270 or 30-06. I have often regretted not getting a 270 or 30-06 for this reason. I think these offer a better value to the survivalist who is more concerned with versatility and availability of ammo then whether or not you can get that extra 50 yards of range.
If this is going to be your only rifle for a while (it sounds like it's your only one), then I'd go with the .308. If the house of cards comes crashing down, it will easier to feed a 308 than a 270. I'd bet that there are 50 rounds of 308 for every round of 270 in the country. The 308 is a heavier bullet so it should have be penetration of cover, and better suitable within any range you'd be inclinced to shoot. 270 is a great hunting caliber, but I think the .308 is much better for general purpose.
Compare the 2 using bullets of comparable ballistic coeffcients using the 130 X in 270 and the 150 X in 308
At 400 yards...
270 velocity is 2186 fps
308 velocity is 2030 fps
The 270 has a whopping 156 fps advantage on paper in the lab. Thats looks good on the surface but lets dig a little deeper and see what that whole 156 fps more speed gets you...
270 has 1379 fpe
308 has 1370 fpe
Thats just what I thought, there is a horrendous 9 fpe difference. Unless you splitting hairs your target will never know the difference I assure you! Heck there is often that much difference from one round to the next from the same box of ammo of the same lot of ammo!
270 with a 100 yard zero will drop all of 20.4 inches at 400 yards
308 with a 100 yard zero will drop all of 22.9 inches at 400 yards
There is a whole 2.5 inches of difference at 400 yards and most people cant even hold a gun still and solidly enough to shoot good enough with either at that range and see any difference! Bottom line...if the 308 aint good enough accuracy, range and knock-down power wise, a 270 will likely offer very little if any improvement for you unless your in the lab doing testing under strict controls.
Now lets look at a factor I dont think anyone really touched on...wide bullet selection by design and weight. Here is where the 308 winchester really shines! For the 270 I think I counted 5 bullet weights from 100 grs to 150 grains. Now for the 308 I counted 16 I believe it was and they range from 110 to 200 grains. Now that offers a world of vesitility. Consider too when a manufacture brings a new line of ammo or bullet design on the market what caliber do you thing its often offered in first? 30 cal!!! Consider too that the 308 comes in a short action rifle VS a long action for the 270. That means that you can get a gun that often a tad bit lighter, and even more so when looking at ultra-light models. When it comes to consistent accuracy potential, the short action in 308 has an advantage over the 270's long action as it is stiffer and as such flexes less under stresses of recoil. This is of little consequese unless your trying to build a real tack driver of a rifle for some serious prescion work at long range, such as a sniper/tactical rifle. We have already talked about ammo availablity in hard times, so I wont beat that dead horse or give it CPR again.
Hey dont get me wrong, the 270 is a fine round and often has good accuracy right out of the box, but so does the 308. Both have great knock down power at distance and both can shoot much further effectively than most people will be able to master enough for one to have an advantage over the other.