I don't have space for a larger case so need to find a solution for the Silverstone GD09 and was looking to use the Noctua NH-C14S cooler as their website indicates it can handle a 12700.
Would I be better dropping down to the i5-12600 CPU instead?
I don't do any gaming but want the PC to be able to handle 4k@60Hz video streaming and video editing as well as basic internet browsing / MS365 work.
I currently have a 7 year old i7-4790s and as I'm paying out to upgrade my PC I want to feel that I'm getting a definite upgrade in terms of performance. Would the 12600 still feel like an upgrade against what I have now even though I'm moving from an i7 down to an i5?
If you have a look at hardware unboxed's review of the 12700, keeping it power limited doesn't lose that much performance, but it depends on what you're doing with it. If those tasks use QuickSync at all, the i5-12500 and up have 2 codec engines (other CPUs only have 1). The 12600 (in comparison to the K, or the 12700) drops the e-cores, so it loses quite a bit of multi-threaded performance (even though it has a lower power budget), which might hurt your video editing. The 12500 or 12600 would be easier to cool than the 12600K and 12700 at full pelt. The 12400 is the easiest of the bunch, because it has a relatively low turbo clock, but you'd drop a codec engine and I'm not sure if that's a good idea for your workload.
If you got the 12600 it has a fairly high base clock (3.3 Ghz), so you could try running it there and see how it impacts performance, the 12600K has a 3.7 Ghz base clock.
In general desktop use, I doubt you'd notice a lot of difference between the CPUs (4790s and 12500, 12600, 12600K or 12700), but in something like video editing the difference in their theoretical performance is absolutely massive, it would save you a lot of time. Their single core performance is also much faster, so you might notice it is snappier and e.g. loads up some apps a lot quicker).