There are not any Howa Mini's OEM in 6.8 or Valkyrie. Or .30 Rem for that matter. The Valkyrie chambering appeals because I've always though the .22-250 was too over-bore, not to mention the Swift. The .224 WBY would have been appealing were it not for the odd brass. Been a very long time since I looked at it, but what I recall was that it could be formed from .30 Rem if you lost the belt. Hum, this looks vaguely familiar....
I'm nearly set-up for Valkyrie, have an upper, brass, ammo, dies....... Just don't think that I want to shoot the chamber in an AR as my primary focus on it.
Short term I plan to shoot factory ammo. Longer term I want to test both light and heavy. Light for varmints, heavy for distance. I'll twist for the heavies, and accept how the lights behave with that twist.