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I've purchased the following components for my computer:

I already have things like 16gigs of DDR3 ram, 7xxx RPM harddrive (no ssd at this point...), etc.

The GPU I'm ordering is higher-ish-end (There's only a couple from nvidia that are better than it, and they quickly jump in price to $500 and $1000).

My real question is... how much of a performance boost am I likely to see in the newest graphic-intensive games if I were to add a 2nd identical GPU to the configuration using SLI?

Would a 2nd GPU give a noticeable difference? Would I be bottlenecked in other areas instead (like CPU processing power)?

The motherboard states the following:

PCI Express 3.0 x16:    2 (x16/0 or x8/x8)
PCI Express 2.0 x16:    1 (@x4)
PCI Express x1     :    2
PCI Slots          :    2

I'm going to be completely honest and say that I'm not very familiar with the purpose of so many different PCI slots. I couldn't find any motherboards that had two PCI Express 3.0 x16 slots (x16/x16), so if I add a 2nd GPU am I just going to be cutting the allotted bandwidth for each one in half? Will that effectively give me the graphic capabilities of only a single card?

If you can add to your explanation the effects of the different types of PCI slots (And what 3.0 means as opposed to x16, x8, x4, and x1) as well as a general explanation of how SLI causes the GPU's to work together and how much of a boost it provides (certainly not 100% more, is it 80%? 50%? 20%?).

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up vote 1 down vote accepted

http://www.tomshardware.com/reviews/battlefield-3-graphics-performance,3063-6.html

This article gives you a decent indication of expected performance in SLI vs non-SLI configurations.

I think an increase in performance of 60-70% is expected.

PCI Express version relates largely to it's speed. the xYY relates to how many lanes it has. For example if I had a card which required x8 lanes, I could put it in a x8 or x16 slot. If I had a x1 PCI card I could put it into any PCI slot etc.

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The GPU I'm getting states PCI Express 3.0 x16. Does that mean the motherboard can only handle a single card? That doesn't sound right. I must be misunderstanding something... Because later it also states Quad-GPU SLI and Quad-GPU/3-Way CrossFireX Support! –  nzifnab Feb 25 '13 at 23:08
    
Only a single card - per slot. In this case you have PCI Express 3.0 x16: 2 (x16/0 or x8/x8) two slots so you'll be fine. –  Peleus Feb 25 '13 at 23:13
    
One thing that's worth noting, you ask "Would I be bottlenecked in other areas instead (like CPU processing power)?". The answer is that depends on the exact application, settings, and resolution, so your noticed difference may be more or less. IMO a GTX 670 is more than sufficient for 99% of single-monitor situations unless you are really concerned about every last bit of performance (and if you're that guy, you wouldn't bother asking this question because you wouldn't care about the cost). –  Shinrai Feb 25 '13 at 23:48
    
Just one remarks: You gain performance for games which support SLI. Not for all of them. –  Hennes Feb 26 '13 at 1:00
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