I was going to post this myself, the inability to move multiple tabs at once came very close to killing opera for me. I need to have a good number of tabs open for work and beyond that I like to have multiple tabs open for other things. The excessive resource usage by chrome originally pushed me to try opera GX, and while I love it, it would be a major upgrade to be able to move several selected tabs to another window at once (especially for those with more than one monitor).