Performance with multiple client asking for a ton of data was good enough; however, while transfer speeds peaked at 160 MB/s, we actually expected more.
Memory utilization was low; however, such wasn't the case with the CPU as it had quite a hard time during our tests.
The fully populated DX513 unit brought with it a notable performance drop, so should you want to use one, keep in mind that it will negatively affect transfer speeds.
Although XPU utilization never spiked, overall utilization was even higher than with the DS1515+ without the expansion unit installed. With the DX513, the volume's utilization was very nearly 100% over prolonged periods of time.