building new pc

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The SLI will be significantly slower. Check this out: http://www.anandtech.com/bench/product/1130?vs=1355
It's a comparison between a single 750TI and a 970. You could theoretically get double the performance out of 2x750TIs, but that never happens, bank on 50-70% extra for the second card and remember that some games you'll have driver issues and poor scaling.

It's rarely a good idea to SLI or CF low or mid tier cards, and it's basically never a good idea to go dual cards from the start unless you're building a monster rig. SLI introduces a bunch of driver and scaling issues so even when it's cost effective, you'll find most people, including the editors here at Tom's, recommending the best single card you can afford and looking...
The SLI will be significantly slower. Check this out: http://www.anandtech.com/bench/product/1130?vs=1355
It's a comparison between a single 750TI and a 970. You could theoretically get double the performance out of 2x750TIs, but that never happens, bank on 50-70% extra for the second card and remember that some games you'll have driver issues and poor scaling.

It's rarely a good idea to SLI or CF low or mid tier cards, and it's basically never a good idea to go dual cards from the start unless you're building a monster rig. SLI introduces a bunch of driver and scaling issues so even when it's cost effective, you'll find most people, including the editors here at Tom's, recommending the best single card you can afford and looking at SLI for upgrade options down the track.
 
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