Are you shopping for PC graphics card? You will be bombarded with misinformation. Mostly, people are intentionally misleading you. They just do not understand what they are selling but you are the one who ends up being burned. The biggest misconception is that you cannot compare performance by looking at specifications.
Take these cards in completely different price brackets for example. this (GT 640) 4 GB graphics card is only about a hundred dollars but no it is not an amazing deal compared to this 4 GB one (GTX 690) for a thousand dollars. Sure they are both GeForce, they both have DirectX 11, their clock speeds are similar and the RAM amount is the same. However, the thousand-dollar card is easily more than an order of magnitude faster than the hundred-dollar one because these cards use different design architectures.
Here is an analogy, a modern loaded Semi can travel around 1400 miles on a single tank of fuel. In 2009, Ford Fusion Hybrid traveled around 1400 miles on a single tank of fuel. These are similar specs and they are both interesting facts, but they have nothing to do with each other. A Semi has a 200-gallon fuel tank, runs on diesel, and carries an enormous load while that hybrid has a 17.5-gallon fuel tank, runs on gas and electricity, and carries around one dude.
Another flawed method of comparing specifications is to compare across different graphics processor manufactures. The chart above is interesting, sure, but I also have another big word for that starts with I (Irrelevant). Because, it cannot conclusively tell us which of these is better. It just does not work that way.
This not to say that looking to specs is always a total waste of time. When comparing products based on the same design architecture and with similar specifications to each other, relative performance can sometimes be inferred, but even this should be done with great caution.
So, at this point, you are probably getting frustrated. How do we actually compare performance? Real games, you want to know how they actually run on the card that you are looking at. This information is definitely out there. Many websites do graphics card reviews online. However, it is important to find a review that covers the games that you want to play, which is realistic for you. For example, if you have a 1080p monitor, do not buy based on a review where the cards were tested at 4k resolution. However, there is great news. Many sites review graphics cards.
What about all the stuff aside from performance, will it still matter? Stability, heat output, power consumption, and other software features, these are all important to me too. Well, there is a ton of information out there about that stuff too. I will be dedicating a post about that later and I know it can be overwhelming but before you go charging into a typical PC hardware community asking questions like whom you think has the best drivers AMD or NVidia. You are going to start an argument, so at least let me point you in the right direction. In my mind at the time of writing, AMD's key advantages are true audio, project mantle, and great multi-monitor support with their Eyefinity technology. NVidia’s key advantages are their game stream, GeForce experience with Shadowplay, and G-Sync. Moreover, I guess if you want a game in stereo 3D, then 3D vision would also be an advantage for NVidia.
