reticulated stingray or "tea cup". they get between 12-14" max i guess but it takes a lil while to hit that. how wide will ur 6ft tank be? width is most important.
also keep in mind that the max size on retics does not include the tail...retics have very long tails and could easily add another 10 inches (possibly more) of tail not including the disc.
wood and decor should be bare minimum rays need lots of swimming space and they will uproot any plants you have in your tank. gl with the scobina the only person that it seems has them is frank and he lives in germany