Unless one is trying to shoot long, VLD type bullets in a short action, there is no advantage of one or the other.
I was an early user of the 260, my first, a Model 7 SS was booked into my FFL on 10/14/97. The perfect rifle for me, but nobody, retail or wholesale, had any ammo. Necessity being the mother of invention, I bought a set of dies, 100 Winchester/Olin 243 cases, some projectiles from Hornady and Nosler, and reread Ken Waters' article onf the 263 Express. I knew from experience loading for the 6.5x55 and 6.5-284 that the 129 grain Hornady SpirePoint was an accurate hunting bullet and so it was. In either late 1997 or early 1998 I was finally able to get a few boxes of Remington 140 grain factory ammo. Talk about disappointing performance! I was getting around 2,500 fps from a 20" barrel and while I didn't expect it to reach 3,000 fps with a 140 grain bullet, I did think that somewhere between 2,700 and 2,800 fps was doable. I bought the ammo off a dealer's shelf and got ammo from 3 different lots, all of which were slower than expected.
As noted previously, Hornady did a great job launching and supporting the 6.5 Creedmoor and Remington did a really poor job launching the 260. Remington's launch and support was so poor, I have to wonder if someone at Remington purposely made all the wrong choices whenever there was a choice to be made.
The other tangible advantage that the 6.5 Creedmoor has over the 260 is the wide variety of factory ammo from multiple manufacturers that is priced as low as $14 per box at Wal-Mart. I've never seen a box of 260 ammo at a Wal-Mart, never.
EDIT: As launched and for many years afterward, Remington made their 260s with a 1-9" ROT, marginal for many bullets weighing over 130 grains.
