It depends on when will you want to visit US again. You are out of status after condition GC expires. and over 180 days out of status will subject you to the 3 years or 10 years ban of 1996 law after you leave US. If you don't want to come to US in a year or two, a couple of months of overstay should be fine. If not in 3 years, 6-11 months overstay is fine. Your next visit to US should be with HLKV visa or immigrant visa.