Performance is a difficult question to answer because it is very workload dependent. However, I can say a few things on performance:
1. Solaris's EULA prohibits the publication of benchmarks without the explicit permission of Oracle. I have not done any benchmarks of Solaris and if I had done any benchmarks, I could not publish them without placing myself and/or my employer at risk of a lawsuit from Oracle.
2. Block device drivers are known to influence performance. In situations where Linux has superior driver support, ZoL will outperform its counterparts on other platforms.
3. There is a key performance fix in a pull request that is planned to be included in 0.6.4. I have seen benchmarks where it enables ZoL to outperform its counterparts on other platforms, although the other platforms were subject to inferior block device drivers. Before the fix, ZoL performed worse:
6. It is quite likely that I will post a future blog post discussing performance. However, performance is a difficult topic to discuss because it is extremely workload dependent. No matter what I or anyone says, or any benchmarks you see, the best measure of a storage stack's performance will ultimately be a test of your own workloads.