Hello,
I am from Chile but I have experience in american codes. I work for american companies installed in Chile for mining purposes (bechtel, fluor).
First of wall, your example designs, even when they are stamped, dont look safe. At first sight it lacks rebar.
I can do review your designs and prepare for your a proper one for the 6' 6" tall one. I will need information about the backfill or soil, and the materials your are using at your project. If you don't, I can specify materials and a proper backfill.
I am just starting here so I can't give you any insurances about how I do my job but I can assure you it will be done properly. I will base my design in ASCE 7 and ACI 318 as main codes for your walls.
Regards,
Néstor.