I always question benchmarks on ec2 because of "noisy neighbor" effects - maybe that's in the noise, but someone trying to replicate your results would perhaps see significantly different results depending whether their VM landed on a busy node or not... Tag this one #ymmv

+1 on testing uncompressed ZFS

I did see a blog post about MySQL with similar results (at least compression was a significant win) some time ago - disks are so slow compared to what throughput modern CPUs are capable of on these sorts of compression algorithms.