From what I've heard, its usually very beneficial for a 7700k. I plan on doing it to my 6700k. I feel as though I didn't get squat as far as the silicon lottery goes.
Yes, I de-lidded my 7700k ages I ago when I had it. Before it wouldn't go past 4.8 but after it hit 5.3Ghz on benches (5.2Ghz daily) as temps were lowered by 21°C.
I delided my 6700k last week with a razor, applied conductonaut, and then dropped a custom loop on top of it. Havent bothered overclocking it yet, but the loudest thing in my system is my HDD now.... damn thing just sits there humming all day. makes me wanna pull it out rofl.