Serious question
I am planning to buy new GPU for almost a year, have been waiting for Pascal. The rest of my computer is gigabyte x58 ud7 mobo, 980x @ 3,78 GHz and 24GB DDR3... was not really thinking about dumping those, since i think its still decent, CPU about the level of current Skylake 6700...
Not a chance this statement is even remotely true. i7 6700K OC will outperform a 4.8Ghz 2600K by 25-30%, sometimes more in CPU demanding games esp. when paired with fast DDR4 4000. Digital Foundry tested this as well.
Your CPU will get destroyed by an overclocked i7 2600K unless all you do is render/encode all day. Not even an i7 980X @
4.66Ghz can keep pace with an i7 2600K OC outside of rendering/encoding.
vs.
As far as the X99 line goes, i7 6900 makes sense, a case can also be made for i7 6950X if money isn't a factor and you don't want to dual-build an i7 6700K + i7 6900K in the same case. i7 6850K makes no sense as the extra lanes are
worthless. This is a repeat of the 5930K - another worthless CPU SKU. If you can afford $400-600 PCIe SSDs in Triple RAID 0 and 2x GTX 1080, then you can afford to step up to the 6900 and likely a 4K monitor.
For maximum gaming performance with 1080 SLI, i7 6700K @ 4.7-4.8Ghz is easily the best CPU. Even a 4.9Ghz i7 4790K is still up to 10%+ behind a 4.6Ghz i7 6700K in games.
https://www.youtube.com/watch?v=f5lfMogcrPU
For a good balance without breaking the bank, i7 6800K (or a discounted i7 5820K also makes sense).
For a powerhouse machine to keep for 5-7 years for work + gaming, i7 6900K could be a consideration although given how long you've kept your 980X, I think if you are ready to make that kind of a long-term investment, might as well go all in on SKL-E next year. Another option is to see how much used i7 5960X CPUs go for as they could be a nice bargain.
As far as 1080 SLI goes, yet another waste of $ upgrade imho when we know the real Pascal flagship will be 1080Ti and it's going to launch within 12 months or so.
1070 SLI gives you 85-90% of the performance of 1080 SLI. Also, don't even bother going 1070 SLI unless you at least have a 1440p 60Hz monitor.
http://www.guru3d.com/articles_pages/geforce_gtx_1070_2_way_sli_review,16.html
One last thing, funnily, the 8-core 6900k at 1000 does nothing to me, even if felt like paying 1 grand for CPU again, for whatever reason it feels underwhelming. Thats why i kinda feel content to stick just with another six-core at almost half the price.
If you cannot actually use the 8-cores for work, then an i7 6700K or i7 6800K are still great CPUs.
I wouldn't do it personally, it'd just not be enough of a performance jump for me to justify the new platform
I say go for an 8-core Broadwell or wait and hope Zen isn't a flop.
but then again I hate doing minor upgrades, I generally upgrade when the new part can offer at least 2x the performance of the old one.
His CPU would already bottleneck a single R9 390/GTX970 in games. That means he has to get a new CPU if he plans to get GTX1070/1080 SLI or it's absolutely a waste of $. In fact, the CPU bottleneck is so severe that even at 1440p 980Ti SLI are bottlenecked by an i7 6700K without faster DDR4 memory. That means such a setup would be even more CPU limited by Nehalem/Sandy/Ivy/Haswell.
http://www.techspot.com/article/1171-ddr4-4000-mhz-performance/page3.html
All the data is literally here but people keep ignoring it and living in the past.
Even i7 6700K OC is a CPU bottleneck for GTX 1080 SLI at 1440p 60Hz.
1080p scaling =
25% (125% vs. 100%)
1440p scaling =
45% (145% vs. 100%)
4K scaling = 71% (171% vs. 100%)
https://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_1080_SLI/20.html
Just because you have some arbitrary bar that it's not worth upgrading the CPU unless it's 75-100% faster it doesn't mean this is a logical way to keep a modern PC up-to-date. Fact is, the fastest GPUs require the fastest CPU or there is no point whatsoever buying 1080 SLI over GTX980Ti/1070 SLI. With the OP's outdated CPU, for gaming, there isn't even a point even buying a single GTX 1070.