Hyperthreading is a bit overrated by people who don't understand what it does. It doesn't add more cores, it arranges threads for better efficiency in an attempt to keep the actual cores (4 in the case of the 4790k) busy. It's rarely a 30% performance increase. Just like intel says, it depends on the application and how it's designed. Some make use of it, others don't, in some cases it can hurt performance (things like vmware virtual machines).
https://software.intel.com/en-us/articles/performance-insights-to-intel-hyper-threading-technology
https://pubs.vmware.com/vsphere-4-esx-vcenter/index.jsp?topic=/com.vmware.vsphere.resourcemanagement.doc_41/managing_cpu_resources/c_hyperthreading.html
Some tests done with cpu's where the ht was enabled and disabled to show the actual performance gained by using hyperthreading.
http://www.extremetech.com/computing/133121-maximized-performance-comparing-the-effects-of-hyper-threading-software-updates
Even in cinebench, the performance increase in a program that utilizes hyperthreading well gained only an 11% increase in performance. 46s to render the image with ht disabled, 41s to render the image with ht enabled. Not as huge of a difference as people seem to think, it's still just quad core same as the i5's. All hyperthreading does is allows the cores to stay busy a bit longer. Not quite the 30% increase a lot of people think and it's not a guarantee. By intel's own admission it's software dependent and may or may not provide enhancement. It's not something you can count on.
https://www.youtube.com/watch?v=EMbYd4LEggo
Don't get me wrong, the i7's are definitely better cpu's and they're a tier up from the i5's. However being there are different versions of the i7, it's not quite as huge of a leap when comparing an i5 (all desktop i5's are quad core) to a lower end quad core i7 (as opposed to the higher performing 6 and 8 core i7's). Where xeon's are equated to an i7 with slower locked clock speeds and no igpu, the same could be said for the i5. In the case of the 4790k, it's just a slightly higher factory clocked i5 with ht enabled. Since i5's have a 'k' version (unlike xeons for the 1150), they can easily be overclocked to match the speeds of an i7.