How does it compare to .308 for power, range, versatility, availability and price?
1. Power: Under 300 yards, a little less power than .308 Win. Past 300 yards, the same gradually becoming a little more than .308.
2. Range: About the same - the 6.5x55 has a little more range in terms of less drop and better wind-bucking, due to the superior BCs of the bullets.
3. Versatility: 6.5x55 wins - it's arguably one of if not the most versatile centerfire rounds in existence, from varmints to very large game. But the .308 is quite versatile too, with bullets as light as the Speer 100 gr plinker on up to 220 grains or even more.
4. Availability: .308 Winchester wins easily. It's far far more available, though 6.5x55 is somewhat popular and can be found at the larger stores like BassPro, Cabela's, Sportsman's Warehouse, etc., and most large local gun shops, but not Walmart or small gun shops.
5. Price. .308 Winchester is cheaper if buying non-premium factory (Fusion, etc.). If buying premium factory, then about the same, and if reloading, about the same as well.
Don't forget the lower recoil of the 6.5x55 and the superior penetrative abilities of the typically-higher sectional density bullets,
ceteris paribus.