I just want to point out here that when people talk about delidding with skylake, what we're talking about is pulling the IHS off, clearing out the paste that's inside, and replacing with either a higher performance paste (Tgrizz?), or a liquid metal compound (CoolLaboratory Liquid Ultra is the most common here).
You then reinstall the cpu into the socket and PUT THE HEATSPREADER BACK ON.
You can hold the heatspreader on simply with retention clip force, or you can add some silicone RTV sealant in a very thin bead on the bottom of the spreader and then place it on the cpu, and close the retention clip.
Skylake CPUs are indeed too short to be used without the IHS in most configurations, but the difference is very very minimal from using the IHS with a proper liquid metal thermal compound. People report 7-15C drops under full load, which is nothing to shake a stick at at all.