All of the above are valid statements.
That being said, if you really desire something just a bit different, the 6.5-06 is not a bad choice, other than you have to neck up 25-06 or neck down 270Win cases, then fireform and develop your own safe loads.
I used to start with max 25-06 loads for the lighter bullets, up to 120 grain, and with 270Win starting loads for heavier bullets up to 160 grain.
This ensured safe pressure ranges for the rifle I had built at the time on a Model 70Win.
Before you order that barrel, there are a couple of things you want to consider.
First, what is your definition of "long range". If you're talking 500-1000 yards, then you're going to want to shoot heavier bullets with slower powders.
IMHO, nothing less than a medium weight, 26 in finished length barrel of good quality.
Two, it may be difficult to find a smith with a reamer and very likely when you find one that will do the job, you also likely incur all of the costs of procuring a reamer.
Three, if you do find a smith, you might be able to save some money by measuring the distance from your rifle's bolt face to the shoulder of the receiver and talk a smith or procurer, such as Mystic Precision to provide a pre chambered barrel with a "jam nut" so you can set the headspace yourself.
Four, headspace isn't critical, you will be fireforming the cases exclusively for your rifle, so there shouldn't be any need for more than partial neck resizing, until you have to set the shoulder back a few thou. This way, cases will last for a long time and only require annealing after 5-6 shots.
Five, IMHO, a 1-8 or 1-7.5 twist rate is absolutely necessary and will easily stabilize everything from 90 grain flat base to160 grain ELD bullets.
Six, You will likely have to open the feed ramp at the front of your receiver so you can seat the longest bullets out to enhance powder capacity
Seven, Figure out what the overall length of the longest bullets you shoot will likely be and try to get the freebore as close as possible so that you don't have more than .050 in. before the ogive of the bullet enters the leade.
Eight, Make sure the chamber has tight tolerances to help with accuracy and pressure. This is where a match type reamer comes into play.
Nine, make sure the smith doing the job knows the above and is capable/willing to work within those parameters.
By the time you get all of this done, you can purchase a Tikka T3 Lite, chambered for the 6.5x55 Swede Mauser cheaper.
In a strong action, with Lapua brass, the 6.5x55 can be hand loaded to the same pressures achieved with the 270 Win or 6.5-284 safely.
Of course, every rifle is an entity unto itself and nothing is written in stone, so it will be up to YOU to work out accurate loads at higher velocities.
The 6.5x55 will come so close to the max loads of the 6.5-284 or 270 Win, that there isn't a big game animal or Varmint that will be able to tell the difference and the bullet drop at those ranges will be very similar, but that's something you will have to figure out in detail by shooting at different distances and measuring.
Not only the above but the 6.5x55 is likely much more doable on your action, but don't expect it to be cheaper.
UNLESS YOU HAVE THE PARTS ON HAND AND CAN DO THE WORK YOURSELF, IT'S CHEAPER TO PURCHASE A NEW TIKKA OR SIMILAR QUALITY RIFLE IN 6.5x55 SWEDE, than it is to build one.
I know several people with the 6.5x55 Tikka T3 rifles that get 2800fps with 140 grain bullets out of their 22 in bbls, shooting a half moa at 100yds, safely.
I know a fellow with a Tikka T3 Varmint who gets an extra 100fps with any bullet weight, because the barrel is longer.
My go to powder is IMR7828SSC, some folks like H4350 or IMR4350 and H4831 or W760 to name a few.