How much power can I really save ?

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I was wondering how much power I can really save with my 4 monitors setup .
Whatever videocard(s) I choose, in order to have 4 dvi conections for my monitors I will have to use abaut the same power .
For example power consumption for bellow cards alone ( info from http://benchmarkreviews.com/index.php?option=com_content&task=view&id=244&Itemid=72&limit=1&limitstart=10 ) :

- HD4850x2 ( 4 dvi connections) alone use 73 W idle and 180 W loaded.
-HD6870 alone ( 4 monitor connections) = 20 W idle / 162 W loaded.
- 2 cheaper cards HD 4670 uses alone 9 W idle and 70 W loaded . x2 cards for my case = 20W /140 W.

So I will save around 50 W per hour with 2 HD 4670 but the system performance will be much much worst . In my case ( 8 hours/day of use / 22 days ) I will save around 9 Kw/month with HD 4670, which is 1euro in my country.

 

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Actually I have 4 monitors , I use them for trading , I use 4 internet live video feeds + 4 websites autorefreshed with data + 4 applications with charts. I dont know what I really need ,large bandwith or more ram memory. My old 3870x2 (4 x dvi ) was doing well but its dead.

 

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Why should I buy any of those if hd3870x2 its half price,4 dvi , and much more powerfull ? http://www.hwcompare.com/11781/radeon-hd-3870-x2-1gb-vs-radeon-hd-7750/

 

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I was missunderstand. My point of view was that saving 1-2/euro /month doesnt worth it compare with much higher performance those hd3870,hd4850 gives.