I haven't heard of ruby library for WeedFS yet. Need a volunteer, anyone?
Performance subjects to your use cases, read speed, write speed, concurrency? And it's related to disk speed and network speed quite a lot. In general, I feel the performance numbers lose the point since WeedFS usually saturate either the network or disk throughput easily.
But WeedFS is very easy to test. Just start master node and volume nodes, and use the command "weed upload" to add a bunch of files, and then use your own tools to stress test it.