Hello. I’m the Product Manager responsible for QE and CSFLE. Performance is always a super nuanced topic, but in short, both QE and CSFLE offer good performance (or we wouldn’t implement it). QE provides the benefit of expressive queries with a good and well-studied security profile. In your case, it sounds like you’re encrypting fields of long strings (on the order of KB). QE doesn’t have substring search on encrypted data yet (we’re working on that now), so CSFLE with randomized encryption would do just fine. If you have other fields in the collection that you want to be able to search on (shorter strings, numeric, etc.) you may want to choose QE for the document instead and just specify the long strings to encrypted but don’t specify a query type so the encrypted indexes aren’t generated. I hope this helps.