Use local disks whenever possible, SSDs are better than other, try provisioned ops on AWS.
EBS is not a good fit, it is slow and jittery.
No idea for compute engine though, you might want to use more RAM and try to load larger parts of the graph into memory then.
Additional reading: http://structr.org/blog/neo4j-performance-on-ext4
You still should check the other things mentioned in that blog post. Like Linux scheduler, write barriers etc.
Better to set those memory mapping settings manually. And for the 2nd level caches probably check out the enterprise version with the hpc cache.
See also this webinar: https://vimeo.com/46049647 on hw-sizing