If you were to use WebSphere MQ you would need NFS v4 instead of NAS but other than that it fits your requirements if tuned accordingly. I would configure it with:
- Circular logging for performance
- NPMCLASS(HIGH) persists the messages on normal shutdown but can lose them in event of failure. Provides high performance in-memory transfers, deferring write until memory buffers overflow or QMgr is shut down.
- BOQNAME/BOQTHRESH to automatically requeue poison messages after BOQTHRESH backouts.
- WebSphere MQ cluster for workload balancing and horizontal scaling.
- A supported UNIX/Linux platform.
I'm just guessing about the hardware requirements but I've seen very good throughput on average hardware. There are platform-specific performance reports available at the http://bit.ly/WMQSupportPacs page. They are the ones named MP*.
- 8 to 10 GB of memory
- 4-CPU
You'd definitely want to use WMQ v7 for this, on both the server side and the client side, instead of an earlier version.
Full disclosure: I'm an IBMer, I specialize in WMQ and I don't have any comparative suggestions for other transport providers. I trust others will weigh in so you can get a good survey of available choices, though.