Those that know me know that I would vote for the 308 for the context of this post.
Like always, .270 or 7mm pills of equal weight and form factor will always have higher BCs than the 30s but between the 270 and 308, with the vast multitude of options available for the 308, I personally could never see myself owning a 270. With 26" barrels, the right powder and a little patience, and finding 2700'sec with the 185-190 grain bullets is attainable in the 308. Running those numbers you'll find they are impressive for such a small case.
The 185 Hybrid (Litz BC .576G1) at 2700'sec offers 1000 foot pounds at 1000 yards at 5000' elevation and 59 degrees F. with 62" of full value 10MPH drift. The 6.5-284 numbers with the 140VLD at 2950'sec are 984 foot pounds and 52" of drift in the same air.
Now there certainly are more factors than just wind and energy to compare (trajectory, recoil, barrel life, cost and many more etc...) so I would never say this is apples to apples nor conclusive and I certainly am not saying the 308 outperforms the 6.5-284 or is better because there are so many more factors here but it does give you an idea of where the 308 is at today versus 20 years ago. One maybe better than the other in a couple given categories but neither are superior to each other nor does one make the other obsolete. It's a matter of which advantages matter most to you. If barrel life is most important to you, then the 308 is superior over it. If high ballistic performance to recoil ratio is the most important to you, then the 6.5-284 is superior to the 308. I'm only using the 6.5-284 in these examples because it was brought up several times earlier in this thread.
The 270 will have disadvantages and advantages compared against the 308 and vice versa. And that goes with all cartridges.
All things considered, with the current .277 bullet selection (which is getting better), I think the 308, with a fair selection of bullets (185-200+ grains) will hit harder further out than the 270 win. Unfortunately, it will hit you harder too.
Not knocking the 270. Just putting .02$ on my perspective between the 2.