Based on that code snippet, and making some (possibly unjustified) assumptions about the rest of the code, your actual request rate could be as low as 50% of your claimed request rate:

Suppose it takes 0.99s to send REQUESTS_PER_SECOND requests. Then you sleep for 1s. Result: You send REQUESTS_PER_SECOND requests every 1.99s. (If sending the batch of requests could take longer than a second, then the situation gets even worse.)

The issue GP has with app and DB on the same box is a red herring -- that was explicitly the condition under test.