My Wife has a 6.5X55 and it is a fine rifle. I am looking at taking the barrel off my M700VS in 22-250
& installing a 260 tube on it in the near future.
Looking at the original post: 6.5X55 vs 6.5-06, well it depends on how you use the rifle. If you use it in the woods with an occassional 300+ yd shot, & you wanted a 24" or shorter tube & a fairly light rifle, I would use the 6.5X55 & it would do well.
If you don't care if it weighs a little more & you may want to stretch the barrel a little on Elk & such with 300-400 yd. shots a little more often on bigger animals, & you wanted a 24"-26" med. taper barrel for this, I would go with the 6.5-06.
Keep in mind that either cartridge can do both roles. I am merely stateing which I would go with
with said priorities/conditions. In regard to the 6.5X284, it has a small edge over the 6.5-06 for
volume target shooting in accuracy & barrel life, but you need a long action with it too unless you single load & offers nothing over the 6.5-06 for a hunting rifle & gives up a wee bit of vel.
Yes, there is a big diff. in the field, esp. when the 264WM is mentioned. Point blank range numbers
are good for people who don't shoot at a distance enough to learn how, or perhaps they don't much with that rifle. With Range Finders & Mil Dot scopes & or Tar. Turrents, you can "step out of the box" or in this case the 6-8" tube thing & utilize the 6.5-06 or 264 Mag. & still shoot at reasonable, practical, but somewhat longer ranges, if you do the trigger time with a good rig. Point Blank Range #'s don't tell you the real Vel & energy differences down range, which is substantial.
For example, a 264 with a mv of 3,100 with a 140gr.(conservative) will have the same vel. & energy @ 450yds. as the 6.5X55 shooting the same bullet with a mv of 2,800 will have at 300 yards. The traj. diff. can be allowed for(though your margin of error for the 6.5X55 is less), but the difference in killing power & bullet performance cannot be. And the wind drift difference is there also.