Regarding the .223 vs .308 for long range competition, things have change over the last few years.
At the Nationals, the M16 and M15 rifles and their same shape variants were popular in the 1000 yard service rifle matches for several years. The 22 caliber center fire rifles were favored for ranges up through 600 yards and did pretty good at longer ranges. Then a couple of old Navy Team folks broke out their 7.62 NATO Garands and started shooting better scores (winning, too) at the Nationals than the 5.56 NATO rounds the big service teams used. The US Army wanted something to compete with those older rifles. The M1's and M1A's shot higher scores. The Army didn't have any more really good M14NM's to shoot 7.62 NATO handloads. So the US Army Advanced Marksmanship Unit cuddled up to the NRA and convinced them to designate the AR10 a service rifle; the NRA agreed and it's covered in the latest high power rule books.
At this year's Nationals, the US Army team set a team record for service rifles at 1000 yards using AR10's and 185-gr. Berger bullets in their 20 inch barrels. Betcha a bag of goodies their handloads were up the the blue pill pressure range to get enough muzzle velocity to keep that bullet supersonic through the paper 1000 yards down range. 'Course all the service teams have a long track record of loading match ammo way, way over SAAMI and MIL-SPEC levels for the cartridge used.
Palma rifles shooting .308 Win. ammo with 155-gr. bullet are just as accurate as the 1000-yard benchrest rifles these days.