Both are good cartridges.......
If you do ballistic gacking for both, and run the 7x57 to modern pressures, it is pretty much a wash at sub 500 yards. I've gacked those numbers a 1000 times and still shoot my 308. A 308 150 gr TSX at 2900 is very close to a 7mm 139 LRX at 2900 - pick your poison.
