6 and 6.5 mm.
The 6mm-284 and 6.5mm-284 are probably the most ideal for sensible and among the most award winning cartridges right now.
For factory loaded cartridges, the 300 Win Mag, 338 Lapua, 264 Win Mag, 7mm Rem Mag, 7mm Ultra Mag, 300 Ulra Mag, 257 Weatherby, 270 Weatherby and 30-378 Weatherby Magnums come to mind as exceptional long range contenders.
Of course, the Old, 30-06, 270 Win, 25-06 and 308 seem to do just fine in properly trained hands.