Can I Downgrade My PS3 (CECH-2504B)

I have a PS3 320GB. Its type is CECH-2504B with Date Code 1A. My problem is that according to this site i can downgrade it to 3.50 BUT according to MinVerChk i can downgrade it to 3.56. I don't know which is more reliable.
EDIT: My initial firmware was 3.56