Serious question here. I have not found any good comparisons on the internet. I know that the 5900X is all around a better CPU for blended workloads, especially with thermals taken into consideration. I currently have a 9900k running 5.1Ghz day to day with C states and Speed Step all working perfectly. Its a solid chip.
I am really liking the Zen 3 and appreciate that AMD has put out something very competitive and frankly the leader on the desktop. I am also itching for a new build in order to hand down my PC to my son, and his down the line to another. I tend to do builds based on keeping all the machines in the house capable of running most new games. So now is kind of the time.
That said, most of my work is office based and web. I do not need the high end content creation capabilities. And I am concerned that if I upgrade I may actually lose gaming performance. I can play any game at an all core 5.1GHz on the 9900k, and I believe Zen 3 may top out at 4.4-4.6 all core. So what is faster for gaming in this scenario. I'd love a new AMD system....but do not want to go backwards. Without OC, Zen 3 is the clear leader...but I haven't seen many good OC head to head comparisons.
The Zen3 surprised many of us I think with its performance. As of right now today, the 5900x is perhaps the best cpu for gaming in situations where you are NOT GPU bottlenecked. This is the real kicker in this whole discussion. The major question to ask is what monitor do you game on? What resolution do you game at? If you are gaming at 4k for example, then the 5900x and the 10900k (and even your 9900k) will perform almost identical in framerate. Any difference in performance here would be in low single digit percentages, if anything. This is because as soon as the GPU becomes the bottleneck, the CPU is essentially sitting around waiting on the GPU, and when that happens, the processing power of the CPU becomes much less important. At l1080p gaming however or at low graphics settings, this coin flips, and the CPU becomes the bottleneck. Fewer pixels and less data to process per frame means high end GPU's can tear through frames at lower resolutions so quickly, that the GPU ends up waiting on the CPU instead. When this occurs, any difference in CPU processing power can be easily observed, as the CPU will be a 100% utilization, essentially doing all it can to kep the GPU fed. This is where you would see the benchmark differences in processors, and is where the 5900x has beaten intels current best. This is why CPU gaming benchmarks though are always ran at 1080p and low or medium graphics settings, to force a cpu bottleneck so you can observe the differences.
More and more people however and going away from 1080p gaming. Even at 1080p though, some games can enter GPU bottleneck territory if you crank all the settings to ultra, or enable ray tracing if its a game with ray tracing features, and as soon as the GPU gets above 95% utilization, the small differences in power between a 5900x and a 10900k quickly disappear, as both cpu's begin waiting on the GPU. because of this, the GPU is of course WAY WAY WAY more important to gaming than the CPU is. Honestly your 9900k is still a perfect chip for gaming and will be fine for years. I have a Asus Strix 3090 and I have it strapped to a 9700k @ 5.1ghz. I game at 3440x1440 ultra wide resolution. My CPU utilization in many games doesnt even go above 50%....In stuff like 3d mark benchmarks cpu utilization will be around 20%...The cpu is literally just waiting on the GPU. In all of these scenarios my 5.1ghz 9700k will perform almost identical to a 5900x or 10900k. The fact is that almost ALL gaming these days is done in a scenario where the GPU is the bottleneck. You want a CPU with at least 8 cores, but aside from that, its impact on gaming is often minimal. I often see people focus on dumping more money into a CPU and ignore things like their RAM which could make a bigger impact in many scenarios. if you are running basic 3200mhz DDR4 for example, then I would invest in high speed, low latency ram and keep the 9900k before I upgraded a cpu. As I said I run a 9700k (which in gaming performs almost identical to the 9900k even in cpu bottlenecks) But I have DDR4 4000mhz C16 memory strapped to it. Just going from 3200mhz to 4000mhz memory speeds I see several FPS gains, even with the GPU bottlenecked. Efficiency from the CPU becomes super important when the GPU is bottlenecked, and having faster RAM helps make the CPU more efficient by lowering response times, which translates into lower cpu latency reponse, which translates into more frames, and typically higher 0.1% and 1% lows. RAM speed Ive often noticed tends to impact the dips, thus raising average framerate, even if it doesnt always add to the max framerate over a given period.
I say all that to say that for pure gaming perforamnce, the CPU isnt terribly important, especially if you game at anything north of 1080p. If you do still game at 1080p then the CPU will have more impact for you, this is assuming you have a beefy GPU. The stronger your GPU, the more it can benefit from a stronger CPU, for all the reasons I mention above. A strong GPU will take more before it begins to bottleneck. Likewise a weak gpu will bottleneck even at 1080p gaming. It all comes down to bottlenecks, and where they occur, and this is all dependent on what you play, and at what resolution you play at.
For a brand new build however I wouldnt go for anything less than the best. That means I would wait for tigerlake. Intel is just about to unveil their new line up, and it will likely take the crown back from AMD's zen3. I would wait to see how that pans out before jumping into a new build right now only to wish I had waited in a few weeks. What else are you running with this 9900k? A 5.1ghz 9900k is still a gaming beast. What RAM do you have, what GPU?