The Nvidia 520 will run slightly better than Intel HD Graphics. Most people who get a 520 do so because they want to use multiple monitors or do light tasks that need slightly more powerful graphics (such as video editing).
The 520 might be good enough for playing older games on high settings, and newer games on low to medium settings.
If you are willing to wait, and need to buy a new PC, or just plan on upgrading your motherboard, and CPU, Intel future CPU called Haswell with Intel Integrated graphics would have 2 times the performance of the current Intel HD 4000 series of integrated graphics.
I saw a video on YouTube where the Intel Haswell Iris and Nvidia 650M were playing a game side by side on different screens, and they both look almost the same.
The AMD APU/CPU based computers also have pretty good graphics performance for an integrated computer. You can also install an extra video card to increase the graphical performance of the APU.
I doubt that a 520 would be feasible for running BF3. You would have to play it on the lowest settings, and even then it would probably lag. If you stepped up to a 640 or so, that might run BF3 on low settings depending on your processor.
I would suggest this(MSI version): http://www.newegg.com/Product/Product.a ... 6814127611
So far with my tests it can run:
Medal of Honor Warfighter
Crysis 1,2,3
Battlefield 3
Battlefield Bad Company 2
Red Orchestra 2
Ghost Recon Future Soldier
If i'm looking at the right one you are wanting to buy. I would suggest getting the 6570 it's the same price.
I own a GTX 550 Ti myself. Battlefield 3 actually works pretty smooth with my gpu, even on high settings. Although a GT 520 cannot handle this game. As far as i saw on the nvidia website, the only games that the gt 520 can barely handle are World of Warcraft Mist of Pandaria and Fallout New Vegas on low settings.
I would recommend you not to buy any gpu's at this moment and save your money for the GTX 670 FTW 4GB. I'm sure it will handle BF 3 on Ultra High Settings even if you record with fraps without any problems. Just make sure you have a nice proccessor so it does not bottleneck your gpu.
Can people overclock a graphics card by replacing the graphic card air cooling system with better copper air cooling, or water cooling, and installing a better power supply with more wattage, so they can perform higher overclocks to get better performance from the graphics card, and CPU and RAM if they also overclock the CPU, and RAM?
I know that some people overclock their RAM, CPU, and video card for better performance. But, they need to install a better power supply, and better cooling like faster fans, water cooling, or copper heatsinks on their chips.