> The RAID 50 array appears to be the current bottleneck.

Any form of parity RAID is always going to be a bottleneck, and should never be deployed into any production environments this side of 2010.

If your application can gracefully handle IO balancing (and potentially replication) between individual block devices, and handle them dying in all of the weird and wonderful ways that they do, then go with JBOD. If not, then your choices are a mirror (E.G RAID1), or striped mirrors (E.G RAID10).