I too was looking to upgrade my 5820k system to a new TR system back when it was released. Ended up getting lucky on ebay with a Xeon e5 2693v4 for the same price of a TR cpu (at the time). I could then just update bios on my x99 motherboard and have enjoyed the crazy speeds since :) (I already had 64gb ram and they worked fine with the Xeon).
I'm not feeling any differences regarding single core performance at all, so I don't get why this is always brought up, but the render speeds and IR - oh man, I was buzzing for weeks. After a couple of months however, you get used to the speed ;)
So in short: If you can score a cheap high-end xeon you can squeeze much more performance out of your current system. Just make sure to check if the Xeon will be supported after a bios update.