I have two PreSonus units. And AudioBox USB for my home computer, and an AudioBox 22VSL for my gigging setup. There are definitely times when I can feel the latency in the AudioBox USB, but the 22VSL unit is not noticeable.
When you are setting up your audio in Native Instrument products you can see the latency. The 22VSL is typically under 7ms on my i7 4GHz computer with a 128 Byte buffer. My studio computer is typically double that, but I have to use a 256 Byte buffer because it is not as powerful.
You can also easily test your unit. For example: If you send pulses to you left channel, and then patch the L Out to the R IN and use a program such as Audacity to record both, you can measure the number of samples offset and calculate the latency from there.
And I stay away from Behringer like the plague.