Comment by dark-star

it's not that bad. At 120MHz, the PSRAM still gets only around 90-100ns per word in the worst case. If you use some SRAM for caching and do bulk transfers, you can get that down quite a bit. Also you can easily overclock the PSRAM to 133MHt (10 decrease in latency) with no problem, maybe even (much?) more.

normal dynamic RAM back then was at 60-70 ns so it's really not that bad. And YT videos show that it also works fine in practice