NVIDIA has created this handy guide to help you choose the card that fits your needs. It lists the cards from GTX 600, GTX 700, and GTX 900 series and sorts them based on power requirements, Direct X 12 support, memory, and support for features like 4k, SLI, Shadowplay, etc.
Now, running a game doesn’t mean the same thing as running it well. So, technically, you can run most of the latest games even on a GT 720, but that’s all you can do. Just run them, not run them well, at even a resolution of 1280 x 720 in many cases. So if you wish to run games decently, you wouldn’t buy a GT 720, unless you have one of those old CRT monitors with a native resolution of 1024×768 so you can enjoy it on low settings. Therefore, the fact that a GT 750 is called a casual card makes sense given that you can run many things decently on it without the highest detail settings unless you have a native resolution of 1366×768 or around 720p.
This diagram labels cards for “High”, “Casual”, “Medium”, or “Max” gaming, probably based on 1080p gaming. Because resolutions matter. My old GTX 650 Ti delivered more than playable frame rates at almost all games on High settings at 1366×768 without any level of anti-aliasing turned on. But in this diagram, it would most likely make it as “Medium” or mid-range card, which would be right. From GTX 960 onwards, you can enjoy a higher resolution and the framerates get progressively smoother. You can begin to game at 4k with a GTX 980 Ti. This will of course vary significantly based on what game you are playing. But this is, nonetheless, a great GeForce guide for anyone who is confused about which card is the most suitable for their needs.