Goto the URL opera://settings/keyboardShortcuts. There you will see "switch right through tabs" and "switch left through tabs" that are set to ctrl + pageDown and ctrl + pageUp.
You can use the shortcuts as is. Or, you can remove ctrl + tab and ctrl + shift + tab from "cycle forward through tabs" and "cycle backwards through tabs" and add ctrl + tab and ctrl + shift + tab to "switch right through tabs" and "switch left through tabs".
