One of the factors that impacts your overall latency is the additional latency introduced by your audio interface. Not all audio interfaces are created equal. Some have low internal latency for both A/D and D/A conversions while others add more latency than perhaps you might like, so you have to lower your buffer size to get the overall desired latency.
To find out how much extra latency your interface introduces - you can use the built-in Latency Measurement Tool. Click Window -> Measure Device Latency... to measure actual round-trip latency:
To measure, follow these steps:
1.Mute your speakers or turn them all the way down.
2.Connect a physical patch cable from any output from your audio interface to input 1 of the interface.
3.Click the Measure Latency Now button.
4.The result will appear in the Measured round-trip latency display.
Note: make sure you do not use any plugins, and that your input signal is not too low.
Find out more about latency, sample rate and buffer size in our free e-book The Ultimate Guide to Optimize your Windows PC for the Stage.