Unless you got extremely short and stiff hands, command and any number up to 6 (7 is a stretch, 8's right out) on the number row, shouldn't be a problem to reach with jsut the left hand.
While this may work efficiently for up to 5 tabs, the CMD+TAB (ALT+TAB for Win) style method is a lot better. In the case of Opera, it uses OPT+TAB, so it doesn't clash with CMD+TAB which as I'm sure you know, is used for Application switching.