This example is a little on the oversimplified side, but it should give you enough to get started. After which, I'd suggest some of the fine articles on sites like Tom'shardware to get more of the specifics.
If you think of your video card like a freeway, then CUDA cores would be analogous to the number of lanes in the road, clock speed would be the speed limit, and memory interface would be the number of lanes for exit/entry ramps. More lanes means more cars can be moving on the freeway at any given time, the higher the speed limit the faster any given car is moving, and then if there's say 2 exit lanes instead of 1, you can have more cars getting off the freeway, same as you can have more cars coming onto the freeway if there are say 2 entry lanes instead of 1.
Again, it's a bit of an oversimplified example, but it should be enough to get you started in understanding some of the articles explaining these things in greater detail.
Also I would recommend the STRIX 970, simply because its 780 performance for a much lower price point, not to mention the 970 has never technology and the 0 fan speed is a nice touch, you can get this card for about 350-375 if you are patient. I cant see spending 500 on a single GPU (dont get me wrong ive done it! We all have at one point of another) but with the 970 specs and its ability to OC makes it a winner for sure.
Conclusion - Buy the STRIX, take the difference in money you would have spent on the 780 and put it towards a second STRIX and run them in SLI, or buy some other misc parts you might need.
Hope this help!
