With the Swede's added powder capacity it actually has the advantage.
Less than 2 grains of water isn't much of a capacity advantage, certainly nothing you'll notice in the field. With some brands of brass, or once fired 260 brass, there just isn't any difference at all. Both rounds are poorly represented by factory fodder in the USA, so both fair better with reloaders.
Curly says he wants a short action, and that's a little hard to shoe-horn a 6.5 Swede into. In fact, it really comes down to which rifle you want when you're picking between the Swede and the Remington. If you simply must have a short action, or a Remington, buy a 260. I would love to own a Winchester Featherweight in 6.5 Swede, and I expect that I will, someday.
Having measured capacities of .260 Remington, 6.5x55mm, and 6.5x57mm, there just isn't any reason for a handloader to pick one round over another in terms of actual field ability, given similar twist rates in the rifles used (so again, it comes down to which rifle, not which round).
For a non-reloader that likes variety and doesn't mind a larger action size, the 6.5 Swede is the way to go, I guess. Most of the Swede ammo is loaded below its ballistic potential here, and the weight range of factory loaded bullets isn't much different from what's offered in the 260. It's easier to find 120 grain factory loads for the 260, but it's a little easier to find factory loads with bullets over 140 grains for the Swede.
Longevity for factory offered fodder may be the biggest stumbling block to buying a 260, for the non-reloader. The 260 has been around as a wildcat for almost as long as 308 brass has been available. Factory ammo has only been around since 1997, and it peaked at about 7 or 8 total offerings from Speer, Remington, and Federal, a number that's since dropped in half.
Mostly, they're both offered with bullets of about 140 grains. They're two peas in a pod, both excellent rounds, and if you've got your heart set on one or the other, don't let folks talk you out of your choice.
