I would be curious about 7mm-08 and 243 personally. They are the same from the neck down so I Would think they'd feed okay. 338 Federal is another story, not sure how the "over sized" neck and bullet would fit into the mag.
260 and 6.5 creed are different animals in terms of shoulder length and angle.
Regardless, in for results if testing is done. I keep telling myself I want a D50 but for the price I can buy about a half dozen pmag 25s.