To add to the point above: honestly you dont need to spend a fortune on fancy heatspreaders or RGB. I'm really happy with these more budget-friendly options that still use the good Hynix chips:

• TEAMGROUP T-Create Expert Overclocking 10L DDR5 6000MHz CL30
• Corsair Vengeance DDR5 32GB 6000MHz CL30 EXPO I've had zero complaints with the Teamgroup kit in my build so far. It just works. Tbh I spent more time yesterday trying to figure out why my desk lamp was flickering than I did setting up the BIOS... turns out I just didnt plug the power strip in all the way. My brain is basically mush after staring at cable ties and zip ties for three hours. anyway but yeah, 6000 CL30 is definitely the way to go for the 9900X.

^ This. Also, unfortunately, many people think buying the fastest kit on the shelf is the play, but it's really not as good as expected on Zen 5. Pushing past 6000 usually forces the memory controller into a 2:1 ratio, which introduces a nasty latency penalty. You're basically trading responsiveness for bandwidth you wont even use. Stick with high-quality Hynix A-die kits that support EXPO profiles. I've had issues with stability on some Micron-based modules at these speeds, so it pays to be picky about the actual chips on the PCB.

• G.Skill Trident Z5 Neo 32GB DDR5-6000 CL30-38-38-96
• Corsair Vengeance RGB 64GB DDR5-6000 CL30 If you try to go higher, you'll likely find the Infinity Fabric just cant keep up without significantly more voltage. Better to have a rock-solid 6000 CL30 setup than a 7200 setup that crashes or performs worse in real-world tasks.

DDR5 6000 CL30 is the sweet spot.