Actually, Endowus came up with a fairly interesting way of doing it in one of their recent articles. They looked at the 3 matrices of SRS top up and concluded that even at 7% tax bracket, under most scenarios (based on a reasonable 7% return), it is good to top up your SRS account.
They did not consider the fact that SRS investment is limited and higher cost than what you can do with cash, that limited benefits you get from 7% tax savings is not enough. 11.5% tax maybe still worth the effort.
