It's delidded, this CPU isn't a great overclocker.
That's 400mhz over my 6700k at the same voltage and about 66.5% faster (+11% per-core, *1.5 for core count). It's on a newer encoder version so that may have changed the performance slightly. Temps are ~10c higher even though it's delidded, they were ~25c higher on this voltage without the delid on either CPU!
It's hard to say exactly how lucky it was on the silicon lottery compared to other CPU's - there isn't an AVX offset while lots of sites and overclockers are dropping their CPU core frequency by 200mhz under such loads so they're not getting the advertised clocks while encoding or even doing some basic stuff like running a web browser or certain games. I ran clock-monitoring software and overlays while experimenting with that setting and the main thing that i found was that people were unaware or lying about what it actually does, the clock drops were very common. I also found that - at least in some circumstances - the non-avx loads that i use would crash the CPU at say 4.8ghz much earlier than the avx programs would crash at 4.7, so much earlier that it wasn't really worth using even a 100mhz AVX offset. A 100mhz offset may be worth it at the very limits of CPU stability, i haven't tested it much up there yet.
It really doesn't want to go past 4.9 HT on, 5.0 HT off without absurd voltage scaling (like +0.1v for 100mhz) so not worth fighting for a 24/7 overclock. It's at its limit and it's better to respect that and be super comfortable at 98% of max performance instead of pushing alll the way to 100% unless you have a large sack of money to throw away.
The other CPU sample that i tried would do 100mhz more (5.0 HT, 5.1 non-HT) with 24/7 level voltages but i kept it at 4.8ghz with HT on because it wasn't delidded and the temps would be impractical at 4.9 and out of range at 5.0 with HT. The 5.1 HT-off was passing its tests at 1.35v nice and cool - could possibly delid that one and bring it back in the future.
8600k's in general will OC very well - turning HT off helps temperatures more than delid and both of my CPU's seem to clock 100mhz higher on the same voltage when HT is turned off; siliconlottery.com reports 8600k's achieving higher clocks through lower temperatures and better voltage scaling even when their 8700k's have delids to control temperatures at max OC's - without that, the 8700k's will overheat but the 8600k's won't so the gap will be larger. It was trivial to run at 5.0 - 5.1 ghz HT-off solid stable (~1.31 - 1.37v with low temps) without delid.
The RAM is a decent bin of Samsung B-die and works fine at 4000 17-17-17-38-2t with all of the secondaries set, i have vccio at 1.2v and SA at 1.225v; they can likely be lowered a bit but the previous 8700k needed at least one of them to be that high. XMP wanted to put some of them over 1.3, no good!
There would seem to be a motherboard limit here since my motherboard has a 4-DIMM layout; the higher end boards which can routintely clock past 4000 (like 4400) such as the maximus X apex are more expensive (+£70 here over an already costly board) and have only two DIMM slots; it'd also likely involve pushing vccio/SA volts up a bit high, maybe uncomfortably high to take advantage of such clocks beyond 4000.
That 4000mhz is very strong and nice for a 24/7! The RAM itself is very comfortable, running at 17-17-17 on 1.39v down from the rated/common 19-23-23; mobo just can't seem to POST with anything over 4000mhz no matter what. This is already technically a 50% overclock on the IMC and boards, it'd seem to be where the limit is for now!
I have two profiles for the RAM, one bandwidth-optimized (4000 17-17-17-38-2T achieving 57,009 MB/s at 41.2ns) and one latency-optimized which is slightly unstable at the moment (3733 16-16-16-35-1T achieving 55,700 MB/s read at 39.7ns). The games that i play usually scale from bandwidth and not latency (SC2, WoW) but some games and programs out there scale from latency primarily (source engine, cinema 4d). That being said, the bandwidth and latency are simultaneously excellent on both setups ;D
I actually haven't tried command rate 3, it wouldn't POST past 3800 with CR1 and if 4266 on like 18-21-21-45-3t would work then it'd probably perform great for bandwidth benchmarks but i don't think i could get a better 24/7 setup out of it. (Edit: Tried that with RAM voltage, vccio & sa bumped up - got my first POST at 4133 but with terrible performance, no POST at 4266)
The uncore can quite possibly clock a bit higher, i just based it on what the other CPU sample could do and then knocked a bit off for safety so i'l have to check it closely in the next few days. Uncore/L3 performance rarely makes significant impact on benchmarks, it's nowhere near as important as CPU Core or RAM. It's also a bit annoying to test, it could run a lot of stuff okay but fail like one test unless you reduced it by 200mhz so it initially gave me some troubles that weren't easy to diagnose.
I have done some RAM benchmarks and i'l do some more, post about that incoming soonish. Quick one for SC2 to make people interested i guess ;D