Yours is a bit of an odd case. But, I see a group of late March to April applicants that are still waiting for SA. I thought March and April applicants got most of the stuff done already. I sent my application in about 2 weeks later than you, and got SA already. However, some people even got PR although they sent applications much later than I did. So, you cannot compare the cases based solely on the time application was received in Ottawa.
Anyway, there is no definitive time frame for receiving SA. It also depends on the case as well. If CIC is waiting for information from the provincial government to check if you or the person you sponsored before received any government assistance, for example, then it could take some time to get that information. I also suspect that the processing of applications will slow down a bit as we get closer to the holiday season, as it is the time for most employees to take annual leave.
As with any government departments and agencies, there are some employees that work at a very slow pace and there are some that are lightning fast. If your application happens to land on the snail paced employees, I'd recommend fair bit of meditation to practice patient and weekly calls to CIC call center.