both are descendants of the 06 !...................
Uh NO the .30-03 came out two before the 7.92x57 !................Theoretically, they (30-06, 308, 243, 22-250, 250-3000) are actually all descendents of the 8x57, the original 0.473" -rimless cartridge.
But back to the point, of the two the OP asked about, the 243 is the much better choice for 500+ yard shooting.
Matt
But didn't the Rough Riders face the 7x57 in Cuba?
The 308 essentially a shortened 06 case.
But the 308 is also a long necked 300 Savage. And the 300 Savage shares the case with the 250 Savage which is the parent case of the 22-250. And then, the 6.5 Creedmoor is a 250 Savage improved necked up to 6.5 mm.
The next question is how many angels can dance on the head of an 30-06 case--or is that a 300 Whelen Express...