I am T2 and tested at 5.2 on my last test in June. I also follow a strict diet. A 5.7 IS diabetic. The 5.7 converts to a 117. Normal blood sugars for non-diabetics is between 79 and 100 (99 is actually the upper limit), which translates to 4.1 to 5.1, The A1c is a 90 day average. I have found that my fasting BG is about the same as my A1c.
You can use this tool to calculate
eAG/A1C Conversion Calculator | American Diabetes Association