XtremIO is targeted for Hot/Warm splunk buckets which is typically recent searches/dashboards, high random reads, sequential reads/writes. As far as best practices are concerned from the storage perspective there are none. XtremIO is an AFA that requires no tunning, no raid configurations, stripe sizing etc with simple management and lots of awesome data services for data efficiency and consistent performance.
Here is a published EMC Reference Architecture for Splunk, with XtremIO and Isilon using
Bonnie++ which Splunk recommends using to simulate indexing and querying.