Apart from the above mentioned options, there are two other ways to help distinguish between two cards, and ultimately, a much more effective way to determine if the game can run on your system:

Direct X Compliance

Direct X is an interface designed to make it easier to speak directly with the graphics card. It is a popular means to 'standardise' the graphics; in complete contrast, early games would actually list all supported cards, and you would have to read through and confirm that your card was directly listed.

If a game lists itself as requiring a "Direct X 10 compatible card", you must have a card that supports Direct X 10, at the very least. Even if your card outperforms the physical requirements, Direct X sort of becomes the language, and earlier cards simply would not understand everything the game attempts to do.

"Let me google that for you"

It surprises me how informative a google search can be, on matters of graphic card support. I always use the format of "(card one) vs (card two)", and am always met with some good comparative statistics from trustworthy sites.

Most of the time, the comparison is detailed enough for me to understand if one card would outperform the other card. I can see how the layman might still find the information confusing, so this comes down to how well you understand graphics cards and the physical requirements behind gaming.

In this particular case, the first hit is a comparison made by UserBenchmark.com. In this case, your card outperforms the required card in all tests. The site even goes as far as commenting on what each performance test implys;

For example, your card outperforms the required card in lighting by approximately 500%. UserBenchmark defines this improvement as "Hugely better.. peak lighting effects, peak reflection handling, regular lighting effects and regular reflection handling". In this particular case, this tells us that your card should be able to handle the lighting effects of the game, and can probably handle lighting at a much higher level of detail, if you have the option of upgrading the lighting quality through the video options.

Try it for yourself

This is the best way to see if your system can handle the game. Try it out, for yourself. Either way, your system should handle it, or not. You won't blow up your card by trying to run a game that requires a faster unit unless you try really hard.

This can be difficult, depending on the game; Game demos are your friend. If a friend has a copy they can lend or give access to, even better.

In the case of Heroes of the Storm; the game is free to play. Try it out, it should run. If it does not, it is not like you have spend money on a game you can not play.

Sites such as System Requirements Lab and Post Stupid have software that you can download and install.

With the software installed, the website can determine whether you are able to run the game or not.

Just compare the video RAM of your GPU and the GPU the game requires.I know there are other things to consider as well but most of the time,the difference is just the vram. So just google search for the gpu your game requires and look for video memory or vram and compare.