The only two advantages I could see of the 6.5x55 over the 308 would be one lower recoil and possibly an advantage over 500m stalking deer. Other than that the 308 has quite a bit more energy with a short action case, mostly less powder, makes a bigger hole, can use heavier bullets. Seems less finicky with ammo (they say a 308 shoots nails) and has the advantage of more ammo available. In Ireland some stalkers had to use target ammo for deer as nothing else was available for the 6.5. The swedes were stuck with this cal and had to make do on Elk etc. I think it is a disgrace, the cartridge needed heavy deep penetrating bullets such as the lapua mega, which are now often used on smaller deer. These bullets mostly just pencil through if they don't hit bone with runners as a result.
Sorry I have spent enough time and ruined hunting days trying to find deer shot by the 6.5 that I won't hunt with anyone using one anymore.
I think it is much easier to choose or getting a 30cal bullet to work properly on the deer than the smaller 6.5 . I believe the 6.5 will work with the right bullet choice and the right man at the tiller however many do not have the know-how and just pick up a box of ammo or a box of what is available at the gun shop, with a 308 one will have a much better chance of picking up a cartridge that will put the deer down quicker. Why would we want to let the deer suffer unnecessarily.
I stick with it, for deer stalking the 308 is better in theory and better in the field than a 6.5x55.
edi