Question about HW Buffer Size

[animas3D]

Hello, I got Pro Tools 10 and I am using it with a Lexicon Alpha audio interface.

When I open Playback Engine in the Setup menu, I get a list of different HW Buffer sizes such as 64, 128, 512 and 1,024.

I noticed that the lower sizes give less latency when recording, however when I set it to 512 and clicked Minimize additional I/O latency, that seemed to remove the latency as well (without clicking it, I could hear latency at 512).

I would appreciate any thoughts about the right setting for HW buffer in the Playback setting dialogue. What should I set it at and leave it at, a low latency or a high one with the check box checked?

Thanks!