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What graphics card do you have and what resolution do you play at??
One word of advice - if the games you play all seem to run fine,then don't bother. The longer you wait in CPU land the better the upgrade you will get.
When PC's first came out, power usually doubled with each release of a CPU. That was noticeable. But as the relative power increases started to decline, 50% was about the lowest increase you would notice an overall increase in speed with your PC. 30% was definitely "not sure it's faster" and it was soon after that everyone started to rely on benchmarks to tell us whether the latest generation was faster or not. Today I think that generally it's a good idea to miss one generation, if you want it to be "noticeable" without using a benchmark. So yes, I think it's time to upgrade. The difference between a 2700 and 8700 should be tangible. Of course, as with everything, it depends what you use the CPU for ~ if you are trying to achieve crazy frame-rates, or you have a slowdown in a particular application, then yes, it will make a worthwhile difference, but if you are already happy then no, it's not worth it.
With a 6 core Coffee Lake and 1080Ti at 720P max settings. In more realistic tests with anything other that type of config then you will see very different results.