If one card gets you 60fps with a game, and the other card gets you 56fps with the same game, I guess you could say that technically the first card is faster. In reality, they are the same. If you saw two monitors side by side running that game and someone asked you which one was 60fps and which was 56fps, you'd have to guess because they'd look the same.
In a situation like that I'd look at my needs. Do I have the power supply to power even the most power hungry card, or do I need to pick an efficient card? Which one cost less? That's how I'd decide. I wouldn't worry about 3 or 4 frames per second differences.