How is it possible the i5 "Quad Core" iMac from 2017 is FASTER than the i7 "12 Core" model?

[h4lp m3]

Unless I'm reading it wrong, Everymac proclaims that the 3.4 model is faster at multicore tasks than the rest of the "Mid-2017" 27-inch lineup. (including the 4.2GHz i7!!!)

Also, you can see that the 6-core is slower than the 8-core in multicore. How does this work?

 

[wilberforce]

I think you are reading it wrong, as I don't see anything unusual in this comparison.
The percentages plus or minus are comparing computers in the first column with the computers in the second column, not comparing computers in one row with computers in another row.
Also, the statement you highlighted in yellow is comparing 2017 iMacs with 2013 Mac Pros, so is like comparing apples with oranges.
I think it would have been clearer if they had just listed the actual scores for each computer, not the % plus or minus.