I am no expert on this subject but there is a reason the .308 is used my snipers and competition shooters, its the same reason the 6mmbr is used and has won more bench rest competition than anything else. Its the short case, short cases offer better efficiency and consistent powder burn over a longer case.
On that note the 6mm's are taking over in 1000yd matches. Even the .243 straight winchester is doing pretty damn good and winning matches. 6mm have great BC's and are super flat shooting.