For the record, fixing latency first isn’t a mutually exclusive thing from CPU and other performance tweaks. They typically are very much hand-in-hand, especially with SQM in play. SQM when tuned a bit provides excellent improvements in overall latency, but it comes at the expense of CPU processing to shape your flows. Don’t discount CPU at this point thinking you can just deal with it later.
Also, if you really have read through many of the other R7800 performance threads, you should have seen mention of CPU governor settings. Don’t assume that’s a “later thing” either. If you want packets to move from WAN to LAN and back faster, your CPU has to be fast to get the packets processed. Again, SQM needs CPU power, but the faster your CPU ramps to full-speed also plays a part in that. Therefore, go back and look at governor settings and things like “up_threshold” and don’t discount them until your latency is fixed.
If you can get some CPU tweaks in place and working well, you might even be able to try cake/piece_of_cake for an even better experience. But, I’m not sure if your R7800 can handle cake on 600mbps of ingress.
Questions for you...
What version of OpenWrt are you running?
Did you look into irqbalance, or some other manual IRQ balancing?
Could you post your SQM config here?
Are the latency spikes random or do you see them only when running a speed test?
Have you looked at your CPU load (both cores) when you notice the latency spike(s)? If so, what kind of load are you seeing?
What is the actual measured speed you are seeing during a wired speed test?
FWIW, I don’t own a PS4. But from some initial looking I just did, type 2 NAT appears to be Sony’s recommendation. Type 1 (open) would indicate no firewall in front of the PS4 which would be a very insecure way to operate. (https://ps4dns.com/how-to-change-nat-type-ps4/#Ps4_NAT_Types)