Revhappy, I understand what you mean, but I don’t understand why you’re using the SGD margin interest rate at IB for these purposes, except perhaps as a guesstimate. If you’re a resident of Singapore IB doesn’t let you buy anything denominated in Singapore dollars (as far as I know), so the margin interest rate at IB is going to be in some other currency, such as U.S. dollars.
You can borrow on margin in a foreign currency, but you take some currency risk on that margin if your perspective is Singapore dollars. I don’t think you can really use IB’s SGD margin interest rate for comparison since that’s the current, “risk free” margin interest rate in that currency. But you’re not borrowing in that currency, not at IB.
I think you just decide whether you want to speculate with margin at IB (in some foreign currency or currencies), and you make the same but separate decision at Maybank KE for Singapore dollar margin.
Another approach if you want to make amplified bets is to use the 2X and 3X leveraged ETFs that are prepackaged for those sorts of bets, if they match, or to use the futures and options markets. I prefer dull, boring, long-term investing that is not trying to beat the markets.