Control-Tab with stacks
Is there an equivalent of control-tab/control-shift-tab that will just rotate through tab stacks (presumably stopping at whatever the "current" tab is within each stack)? I have one stack with 14 tabs on it, and it'd be nice to just pass by it with one control-tab rather than 14. Also, is there any way to re-arrange tabs within a stack without unstacking them all and hoping that they end up in the desired order when I restack them? I thought maybe a click-and-drag on the preview panel, but that doesn't seem to do anything. Thanks!
There are shortcuts for Next Tab (recent) and Previous Tab (recent) .
There's no way yet to reorder tabs within stacks. More options will come in time. Vivaldi is still only version 1.2 while Firefox is up to version 46 and Opera is version 37.
Try the tile stack and untile stack shortcuts to find tabs within a stack quickly.
"Also, is there any way to re-arrange tabs within a stack without unstacking them all and hoping that they end up in the desired order when I restack them?" –> Yes, but not with entirely native V functionality [yet]. Use the extension TabsPane, with which you can drag the specific tabs via their TP thumbnails. It removes all the guesswork.