I have spent an enormous amount of time over the past couple of weeks tuning ZFS to give us the best balance of reads-vs-writes, but the biggest problem is trying to find the right benchmark tool to properly reflect real-world usage. We are currently using FIO but sheer number of options (depth queue, numjobs, libaio vs io_uring) makes the tool unreliable.
For example, comparing libaio vs io_uring with the same options (numbjobs, etc) makes a HUGE different. In some cases, io_uring gives us double (or more) performance than libaio, however, io_uring can produce numbers that don't make any sense (eg: 105GB/sec reads for a system that maxes out at 72B/sec). That said, we were able to push > 70GB/secs large-block reads (1M) from 12x NVMe drives which seems to validate ZFS can perform well on these servers.
OpenZFS has come a long way from the 0.8 days, and the new O_DIRECT option coming out soon should give us even better performance for the flash arrays.