The "K" designated processors would only be more prone to throttling if the power or cooling solution is insufficient. The "K" designated processors have the unlocked clock multiplier. The "K" designated processors are sourced from the highest yield wafers at the manufacturing labs and as such, statistically, would be more reliable and more efficient, statistically.

It also depends what you are going to do with the computer.  If a heavy gamer and a tinkler, the KF gives you the opportunity of over clocking.  If doing normal everyday tasks, the F series is just fine.

I would pass on both and get a 7950X3D, which on average performs better and draws less power than the Intel counterparts.

AMD versus Intel 

Yeah that's what I was looking at, although I will probably get the 7900X3D. It's currently $589 on Amazon. I'm looking for an aluminum case that will take a 13" + GPU.

I have a Lian Li Lancool II Mesh and I like it. Really good cooling and very easy case to work in.

It supports up to 384 mm GPU length. (15.1 inches)

There's a new version that has likely some improvements.

If you are dropping to that price point, then based on the linked performance comparison you would be better off with the i9-13900K.

Those R15 packages with the 13900F cpu are air cooled.  My old R13 with the i7 thermal throttled in some games with the cryo-cooler.  I can't imagine how this one runs being air cooled.

If you are dropping just over $3k, you can build a very nice high end system yourself on a z790, 4090 oc, 32gb 7000mhz ram, 360mm cooler, etc...  Go for the i7-13700k they easily run all-core 5.5ghz for hours without throttling, and with some slight overclocking on even a base motherboard can make it up to 6ghz (several videos show how). 

Yes, I saw that as well. I created the topic more as an observation that the 13900F is not a bad gaming CPU. It's more energy efficient than the KF variant. It should theoretically throttle less. I am not in the market for a new Alienware. If I decided to go prebuilt again it would either be an HP Omen 45L or an Origin PC (former Alienware group).

I'm leaning on a DIY and waiting for prices to drop in the next few months before I decide.

Using less energy to do less work is not the same thing as "energy efficient".

When I buy a gaming rig, it is to do 100% gaming on it. When I want to do work on a computer I use a laptop or a Mac. Just viewing the gaming benchmarks on an F and KF variant, the FPS are extremely close which then gets into price vs performance. If I were to buy a 13900F or 13900KF, it would not be for 1080P as my target would be 4K and minimum 60FPS, which at that point things lean heavily on the GPU. A 13900F can easily handle any RTX 4 series GPU including the current king, the 4090.