Ian,
If you are able to plan in the change from RAID 5 array to RAID 1+0 for the datastore hosting the LEM appliance, I strongly recommend this. If this is not feasible of course, then you will need to carefully monitor your disk I/O latency to see if problems persist in 5.7.0. If you don't have many nodes and not a high rate of events per minute, you shouldn't see an issue except potentially when running nDepth searches spanning over date ranges greater than 24 hours, as this requires compressed data to be decompressed and written to memory to then be searched. You can imagine what this does to disk I/O and in turn your latency.
Garreth