I don't have one. However I have 8 or 9 or 11 Weatherbys and looked it up from a historical perspective long before it was announced. It's been around a long time.
If you buy one in a Weatherby Mark V, now, you should get sub-MOA guarantee.
Virtually identical to a 26-Nosler for the belted magnum and Weatherby lovers.
I don't have a 26-Nosler either, just 277/26-Nosler, 28-Nosler (well I sold it), 308/26-Nosler and 338/26-Nosler. Same as I have a 257 Weatherby, 277 Weatherby, 7mm Weatherby, 300 Weatherby and a 338-378 on the way.
So basically it boils down to my educated guess.
If I were going to buy a big magnum 6.5 I would have one heck of a time choosing between a 26-Nosler and a 6.5-300 Weatherby except.... I like Weatherby.