If you can afford it, mirroring in some form is going to give you way better read perf than RAIDz. Using zfs mirrors is probably easiest but least flexible, zfs copies=2 with all devices as top level vdevs in a single zpool is not very unsafe, and something custom would be a lot of work but could get safety and flexibility if done right.

You're basically seek limited, and a read on a mirror is one seek, whereas a read on a RAIDz is one seek per device in the stripe. (Although if most of your objects are under the chunk size, you end up with more of mirroring than striping)

You lose on capacity though.