we tried using EFS for shared storage but quickly depleted our I/O bursting credits and our throughput dropped to a grinding halt, because our app's worklaod is both disk write and read intensive. No solutions yet
If you need more performance than EFS for your shared filesystem storage, you could give our ObjectiveFS (https://objectivefs.com) a try. We see significantly higher read/write performance, especially for smaller files.
Unrelated, just some color commentary, I put my first request that took over 24 hours to be approved... 150k+ provisioned iops. Seems they don't like doing that.