Not the perfect solution, but...
If you right-click on a tab, you can goto "save" and choose "all tabs as a speed dial folder". Then, you can later right-click on that folder and choose "open all in tabs" or choose to open all of then in a certain workspace.
In addition to that though, if you use ctrl + left-click to select multiple tabs, when you right-click on one of the selected tabs and goto "save", it'll say just "tabs as a speed dial folder" where it will just save the selected tabs to a speed dial folder.
You can also give those speed dial folders a name if you want. And, at the URL opera:/bookmarks, you can move the folders from the speed dial folder to somewhere else if you don't want them on the startup page.