The MongoDB Performance team aimed to improve repeatability in performance tests on EC2 instances by measuring noise and making configuration changes to minimize it. They found that IO performance was a key factor, with EBS instances proving stable options, particularly when using Provisioned IOPS. The i2 instance family showed promising results in focused IO tests but was less ideal due to unstable MongoDB performance. Switching from ephemeral to EBS disks in production led to more stable performance and reduced day-to-day variation in test results.