What the barrel twist? The effectiveness of going heavy/light for a particular caliber is mostly about what the particular rifle can/will stabilize per it's twist rate.
The Sectional Density of the 6.5x55 makes it capable of penetration that rivals the 30-06, though with less punishment of the shooter and with much longer reach for smaller/thin skinned game.
The only down-side of the 6.5x55 is in comparison with the .260. They're so close ballistically that one must consider the .260 and when doing so.. the shorter action, barrel and lower weight of a nearly identical shooting .260 gives the .308-based cartridge a huge advantage in my book.