what`s the cheapest cpu that won`t bottleneck a 980 too hard

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I think a dual core i3 is a poor choice when most new games are demanding a quad core or better CPU. At a minimum I'd choose a low end i5.

Such as an Intel Core i5-6400 ideally or the Intel Core i5-4460 not ideal, at a minimum.
A good overclock-able CPU is money well spent IMO.
I kept my Q6600 for ~7 years pushing it harder and harder till it eventually held my gfx back too much.
Upgrading gfx cards is easy. CPU, not so much. Almost always involves a new board, sometimes ram, and a lot of buggering around.
If you can wait and spring for a 6600K, it will last for many years.
I'm expecting my 4790k to also last ~7 years.
If you've got no choice, the 6100 should see you through the next 3 years quite well, but maybe not more than that if you're upgrading cards along the way.
 
I think a dual core i3 is a poor choice when most new games are demanding a quad core or better CPU. At a minimum I'd choose a low end i5.

Such as an Intel Core i5-6400 ideally or the Intel Core i5-4460 not ideal, at a minimum.
 
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