I wouldn't say that everyone has moved to a small 6mm. If you look at match reports, you'll see that East of the Mississippi anyway, the .30's still rule at 1,000 yards, day in and day out. And in short range BR, the small .30s are gaining some popularity even among group shooters.
The IBS 1K Nationals are going on this weekend, and if I had to bet, I'd put my money on a .30.
But what is changing, as it did in short range BR after the first 10 or so years, is that the chamberings are getting smaller. A number of Pennsylvania shooters are using the WSM, which is what, about 80 grains water full to overflowing? A number of us are using a slightly bigger case, equivalent to the .308 Norma Magnum (88 grains water, full). All of these are significantly smaller than the .300 Weathrby Improved (what, around 98 grains water full?).
So maybe your smaller 6.5 will show you a way to some wins -- certainly when the wind isn't acting up. Further, it should make a fine 600 yard chambering, & I believe there are some of those in the Dakotas.
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Just a caution: As with so many things on BR Central, as Mickey Coleman says, "you have to learn to separate the fly specks from the pepper." If a product, chambering, whatever, is successfully used by a number of people, anyone saying that it is no good, or that one particular thing is better, should probably be taken as giving an advocate's opinion, not a fact. Nothing wrong with advocacy, as long as it's identified as such.
Good luck