What dictates the output latency with a Native Instruments Z2?

I have a Native Instruments Z2. With the process buffer at 64 samples and the USB buffer at 1 ms, these are my latency settings: -

Processing = 1.3 ms
Output = 4.4 ms
Total = 5.7 ms

Someone else I know who is also using a Z2 has the process buffer at 128 samples, the USB buffer at 1ms, but gets better overall latency than me: -

Processing = 2.7 ms
Output = 2.0 ms
Overall = 4.7 ms

So what is it that dictates the output latency? Why is mine 4.4 and his 2.0?

Thanks.

He's probably running at a higher sample rate.

Your CPU, chipset, motherboard, USB controller, OS, drivers.

Processing Latency is sample size and sample rate dependent:
192 samples / 48k = 4ms (my normal setting)

Output latency is hardware, OS and driver dependent. Check which driver you both are using.

My MacBook Air (2011 13" 1.7GHz) has 2ms output latency with the current drivers.