99% of the problem with Mac anti-virus is that if you hang around these forums long enough, you see time and time again that anti-virus packages are at the root of many users problems, and it does not matter which A/V vendor, they have all been the root of a problem (performance issue, kernel panics, blocking access to valid sites, etc...).
The A/V vendors write the packages for Windows, and then hack and slash their products into the Mac without truly understanding OS X, often times using undocumented APIs, or worse just reaching into the kernel without using appropriate kernel locking to access data structures, and then one day the the timing is just right, and boom, the user's Mac panics. Or the OS X kernel release changes, and what they are doing interferes with OS X normal operations slowing down OS X to terrible speeds.
If you want to run A/V solftware, then keep this in mind, especially every time you update/upgrade to a new OS X release, because that is when kernel changes happen, and the A/V packages get caught doing undocumented things in the kernel. Especially in later releases such as Yosemite and El Capitan.
As to getting Sophos warning message over and over again. Maybe you you should consider how helpful the Sophos forum was and use that as in indicator on how well this product is being supported on OS X. Or, since I do now know much about their forum, it is possible it too is only users that contribute there, and then that would say there are not a lot of Mac users participating. If that is the case, maybe you should be contacting Sophos support directly.
