I'm in the same boat and still running my now 5 year old 5820k. It's surprising to think that after all this time there's little point in upgrading.
I will say that when I upgraded from an i7-920 to my i7-5820k in 2014 even then I want sure it was actually worth the money I spent to change. This time round I'm running my 5820k until there's literally something that it can't handle!
My next upgrade will be a new GPU to replace my geforce 980. The CPU should still have years in it IMO barring hardware failure. Even then it'd probably worth repairing rather than upgrading.
It depends if you want to upgrade really. We have chips that will smash a 5820K from as little as £90 now and others that are many leagues ahead.
You can easily make a much bigger jump in performance than a i7 920 to a i7 5820K today.