In Amazon RDS for PostgreSQL, you can provision up to 3TB storage and 30,000 IOPS per
database instance. For a workload with 50% writes and 50% reads running on a cr1.8xlarge
instance, you can realize over 25,000 IOPS for PostgreSQL. However, by provisioning more than
this limit, you may be able to achieve:

A.
higher latency and lower throughput.

B.
lower latency and higher throughput.

C.
higher throughput only.

D.
higher latency only.

Explanation:
You can provision up to 3TB storage and 30,000 IOPS per database instance. For a workload
with 50% writes and 50% reads running on a cr1.8xlarge instance, you can realize over 25,000
IOPS for PostgreSQL. However, by provisioning more than this limit, you may be able to achieve
lower latency and higher throughput. Your actual realized IOPS may vary from the amount you
provisioned based on your database workload, instance type, and database engine choice.
https://aws.amazon.com/rds/postgresql/