I don't have exact data on proving that the .308 is more accurate than the .3006 but I have read them in the past. The articles that I've read used national shooting competition data to prove the point.
Yes there is an often quoted article on the internet that was written in 1983 giving support to the .308 being more accurate than the 30-06, but the information is well beyond dated and only applied to service rifle competitions anyhow.
The shorter powder column is complete bunk- it might have ramnifications in benchrest competition, but then again benchresters are usign very short actions on their rifles to keep everything as stiff as possible. A .50 BMG round which is considered to be an excellent long range round is nothing more than a 30-06 that is scaled up proportionally, the .223 is a 30-06 scaled down proportionally, neither of which people would call less accurate than the .308.
If you look into mil-surp ammo and just general fmj ammo you'll find much more available in .308. I used to buy .308 in amounts upto 500 rounds manufactured by countries all over the world. I can't say I've looked extra hard for the equivalent .3006 ammo but I'd be really freaking surprised
Have you priced any of this surplus ammo out lately? You are in for some sticker shock if you haven't. 30-06 ball ammo is probably easier to find right now with Korean and Greek surplus being pretty common. I wouldn't buy surplus ammo for anything other than plinking myself- it simply isn't accurate enough to shoot in matches with any expectations of scoring well.