As far as I can tell there are no differences in the IHS or ILM for 13900K and Z790 from previous generation.
I'm planning on using the contact frame.

ymmv with the frames, but I can tell you safedisk recommended not using a frame for z790 apex, if that is any indication. I personally do not use a frame and didn't have any issues on z690 either, but my utility is diminished by using a heavy LN2 container for most of my needs. for a daily i'm sure you'll see a bit of improvement in temps with a properly installed frame.

I've been using the contact frame on my Z790 Kingpin with a 13900K for the last week or so since I got it with no problems.

B0baganoosh
I had a ton of issues getting the frame running correctly on the 12900k and previously gave up on it, but I have been running it on the 13900k on my z690 classy since I bought the cpu and it's been great.

Did you do a pre/post bench to see what kind of temp differences you were seeing?

Delirious

djmpsf

B0baganoosh
I had a ton of issues getting the frame running correctly on the 12900k and previously gave up on it, but I have been running it on the 13900k on my z690 classy since I bought the cpu and it's been great.

Did you do a pre/post bench to see what kind of temp differences you were seeing?

was wondering the same thing.  I'm setting at 38C at idle at 5.8ghz.     I think temps top off about 95C at cinebench.  

I am not using the frame atm, but without it I am sitting at 25c but underload I hit 100c and it starts to throttle. This is using a CLCx 360! I had tried to use the frame before on my first board (long story) and had similar temps.

I didn't test the 13900k without it, but I did test the 12900k with and without it. I definitely dropped 6-10°C with the frame in with the 12900k, but I couldn't get it to be stable long term, so I had removed it.
 
What I can say is that my 13900k runs significantly cooler than the 12900k at the same (or even much higher) power levels.
 
I currently have a MO-RA3 Pro 420 and an internal 420mm rad on the case (I know...it's a bit ridiculous at the moment), but I'm idling around 23°C (ambient is around 18.8°C) and Cinebench r23 multicore will drive cores up into the 70's and 80's if I have P-core all-core at 5.5GHz and e-cores at 4.6GHz. I have also run 5.6GHz P-core and still didn't hit 90's. I've tested 5.7GHz all core in r23 (e-cores at 4.6GHz), but I think I started having some cores poke at the 100C limit it throttled to 5.6GHz so I had reset it to just run there (6GHz on 1-4 cores) and had this:

 
I don't see any improvement in games going from 5.5GHz to 5.6GHz all-core, so I just run at 5.5GHz all-core daily (6GHz 1-4 cores, 5.9 5 cores, 5.8 6 cores, 5.7 7 cores, 4.6GHz e-cores). With those settings I get around 40.2k multi-core in r23.
 
Another thing I found when doing a boat-load of tests on the 12900k is that the thermal paste is very important. It makes sense when you think about how much power is involved. Any thermal impedance added by the paste will have a greater impact than on previous CPUs. I have the most luck with Kingpin KPx or Prolimatech PK-3 nano. I haven't tried the Kryonaut extreme (pink version), but the regular kryonaut grey was much worse for me. I also tested Corsair XTM-50 when I ran out one day and it was the best thing Best Buy had locally...it was...horrible. There was a little separation, so it's possible it was just sitting on the shelf at Best Buy for 3 years or something, I don't know, but KPx is so easy to get in good quantities that I just buy that now when I can.