Last year I got a Intel Core2 Quad Q9400 from Dell that came with a GeForce 9800GT. I'm thinking of buying a second 9800GT to run in SLI. I would greatly appreciate some advice--as I'm quite inexperienced when it comes to graphics cards (as my questions will reflect!)
What is the easiest way to check that my motherboard is compatible with running graphics cards in SLI?
Will a second 9800GT result in a noticeable performance/graphics increase for upcoming games (e.g., Mass Effect 2).
Does it matter what brand I go with for the second 9800GT (i.e., should it be the same brand/have the same specs as the one that I currently have in my PC, or does that not matter)?
The easiest way to check SLi compatibility is to run CPU-z and look at the Motherboard tab. It has to be an nVidia chipset to be able to run SLi. Then, you'll have to look at the motherboard and see if it has another PCI-e x16 slot.
Although it won't get you double the performance of one (usually SLi scaling is good, though, like 75-80%), depending on whether or not the game is optimized for it or not.
An identical card is preferable. However, you can go with just about any card, but I would make sure it has about the same clock speeds (the faster one will downclock itself to match the slower one), and with the same type and capacity of RAM.
Also, you need to make sure that your power supply is up to it. Normally OEMs like Dell will put in a power supply that is just barely enough to run what they put in it stock, so check the sticker on the side of it and see what the wattage and amperage is, specifically on the 12v rail.