Look around the forum there were a few threads on how to pay tax. Is your tax deadline April this year or January next year ? If its Jan/Apr next year then i suggest you look at logan's method of using Octopus e-wallet payment.. tough work as you need to swipe the card every day for a year, but you do get 1.5%~2.0% rebate for up to 100k HKD.
As for the remaining amount, at this stage most of the banks credit card offer have ended. They usually offer those from September onwards.. some banks end their offer by December, some are extended to Feb/March. Have to keep track what's available. Most of those are decent giving you around 0.2~0.4% rebate on up to a certain amount of payment. If you are not too busy and enjoy the optimization then just collect a few offers and split them optimically.
But long gone were the days when they give you full asia miles for the 200k tax payment.. Many credit card companies likely got burnt for them since those mileages cost quite alot.