Nvidia has long had a reputation for being the best but also a reputation for being the most expensive. A great example is a top of the line very well performing ATI Radeon card costing between $500~$800 would get you a pretty good Nvidia card, but not a top of the line Nvidia card. Nvidia cards usually come with some pretty cool features to name a few they can make games 3D assuming their compatible with Nvidia’s 3D Vision Kit. Often times Nvidia also tailors their cards to give little enchantments to games to make things pop-out a little more. Awhile back I remember seeing Nvidia advertising how their cards enhanced World Of Warcraft’s environmental elements such as grass making the game feel more crisp and realistic to a degree. Nvidia is a company that delivers on their promises and is always releasing new drivers to help increase performance in the latest games. Sometimes the released drivers can boost performance as high as 50~80%. Overall your safe to buy a Nvidia graphics card you really can’t go wrong you will just have to spend more for their products.
SLI is where you take two Nvidia cards, and link them together in the same system which makes them run together. Running two cards is not always better than one, but more times than none it is better to have two compared to one. Unlike ATI Radeon you cannot SLI two Nvidia cards on a motherboard with a 4X PCI-E slot and an 16X PCI-E it simply won’t allow it unlike ATI Radeon. This however is a good thing I am not sure why Radeon allows one to link two cards in slots with extreme bandwidth limitation difference but they do. SLI can run 8x8x or 16x16x. It is often times more beneficial to buy one powerful card than link two weaker cards, but sometimes the money just works in the way that you can only afford to link two weaker cards. The option is their though so it never hurts.