Unfortunately 9P2000 tends to perform badly over high latency connections. There was talk of writing a new version that would allow clients to group certain messages, but nothing ever came of it.

Edit: I just found a very recent paper on Improving the performance of Styx based services over high latency links (Styx being the Inferno name for 9P): http://gsyc.es/tr-docs/RoSaC-2011-2.pdf