Hi, it really depends whether you want to grow cpf aggressively to help you in yr retirement. Since you have already put aside the money needed for your house and you have NO other purpose to use yr remaining OA money, growing yr SA with OA money is a logical choice. No doubt you can top up yr SA using RSTU. Do note that, top up money can't be withdrawn after 55 even if you have reach FRS. It will be reserved and form part of yr FRS. You can view the money reserved at the last part of section A in yr CPF account.