One site that I found very useful for comparing different cards is AnandTech’s benchmarking for diffferent cards. You can choose the games that you are planning to play and see the kinds of frame rates you will get with high, or ultra settings. Not quite as good as trying them out side by side yourself, but it will give you an idea of whether the card your considering is sufficient for your needs.
Of course once you get to frame rates of about 60 fps, any increases are theoretical, your eyes cannot tell the difference between 60 fps and 80 fps. Do you need something better than “very smooth gameplay with no stutter”?