To get the most out of your Load Test it is best if you follow a few simple guidelines:
Make sure you have think times with deviations. Think Times with deviations have a random duration. By having some users at different intervals sitting out of the test (thinking) it not only mimics real world usage better, but it allows for your agents I/O to not be as congested. It may be counter intuitive, but having your virtual users stop to think for a time will actually increase the number of users and requests that your agent can complete.
Use ramp times to build up your users from a small number to larger numbers. Again, if you start with a large consistent load, without any ramping, you will likely clog the I/O. By ramping up from lower numbers you give your think times better chances to get involved.
Use more CPUs, Test Studio Load Agents are multithreaded, so take advantage of that by giving more CPUs to your agents to increase throughput. In general approximately 8 users per CPU unit seems to be sufficient to have a realistic load testing results.
Use more Agents. The more agent machines you use, the more networking ports you can use at any one time, freeing up congestion on the agent side.