I would take the 55g keep the JD and convicts. Oscar won't work in the long term in a 55g. I know a lot of people say an oscar is ok in a 55g, but they do need swimming space, and the bioload is to much for a small tank like a 55g. I had a friend keep an oscar in a 55g doing 3 water changes a week, and it got HITH and died w/ in weeks of getting it.