From my past SnGing I seem to recall the general advice was play 200 to get an IDEA of where you are at. If you are losing after 200 it's time to really think about your play. If you are winning then things are good. However, it could still be just variance etc. I think around 1k tourneys is a good estimate of your ROI.

However, it depends how many $50 limit Stud h/l tourneys you enter in the meantime.....