I do have Clamxav with Sentry. Sentry by default monitors only the user account which is okay but I agree with the above in that it is really not necessarily. I have not noticed a performance hit but the more that you want Sentry to watch then the more your computer might be slowed. AV software that I tried on my 2012 MBP really did drag the performance. I think that a scan only AV program is all you might want and only in the sense that it might make you feel better.