RAM based on Hynix M could already make ~7400, but the new kits that are using Hynix A will be a bit better and the top bins should reach ~8000. Hynix M can make 8000 too, but at higher voltages which means more heat, and this is a problem in DDR5. 1.4V is still fine 24/7. More depends on the case airflow. So in comparison, memory kits available right now have up to 6600 CL32 1.40V. Memory kits expected to appear in the upcoming months should have 7200 CL34 1.40V. Well, you can set Hynix M at 7200-7400 1.40V too, but at more relaxed timings like CL38.
Even the best 2-slot Z690 motherboards are limited to about 6800. If you have luck, then you get a mobo that can go up to 8000+, but it is quite random, and you can get ASUS Apex which will make 6600 on one slot and 7600 on another one. Z790 is generally rated at 7200+, even in these lower 4-slot series, so they clearly improved something, as I highly doubt it's only IMC. All my 12600k/12900k could make 7400 on one slot, but I didn't have the luck with motherboards, and the best one could make 7000 on 2 slots. Gigabyte Z790 Master, which is a 4-slot motherboard, has 8000+ in the specs.
AMD is releasing everything slower, and I doubt we will see a higher RAM clock anytime soon unless they do something with a 1:2 ratio and higher RAM clocks. I haven't seen anyone who could run RAM at 1:2 6600+ on AMD, and I have no idea what would be the performance hit in this case. On X570/B550 4600+ 1:2 was already giving good results. X670E motherboards have RAM ratios up to 10k.
Tighter timings won't really happen. Manufacturers won't/can't release anything with very tight sub-timings and main-timings are close to the IC limits at reasonable voltages. I mean, we already have 6400-6600 CL32-39-39 kits in stores. 6400 30-38-38 is about max at 1.40-1.45V. 6400 CL28-37-37 is about max at 1.50-1.55V, which may cause overheating without additional airflow. RAM affects the performance even less than in the last gen, so there is no point in pushing it to the limits. You will see the difference between 4800/5200 and 6600+, but not really between anything 6000 and above.
