Read This Thread and there is a link to Visa International Exchange Rate Estimator

Just use your Petronas Card as you would in Malaysia and don't worry about the exchange charges.

If you need cash while in Singapore, use your Maybank ATM Debit Card (if you have one) BUT never use credit card for cash withdrawal as you will be imposed a fee upfront and subsequently daily interest shall be imposed. Furthermore, will it be convenient for you to access a MBB ATM?

There will still be some foreign exchange fee with ATM/Debit/Credit card.

As for cash withdrawal fee (per usage), please call HSBC CS or refer to their website for further info.

Like I said, use your MBB Petronas Credit Card because it has on of the lowest conversion fee for Malaysia issued credit cards.

I used to have the MBB Petronas, click on below links to see my article on overseas transactions and you'll note MBB Petronas exchange rate was the lowest when comparing to my other credit cards.

Overses Transactions - What Card Is The Best? Part II comparing transactions in Singapore.
Overseas Transactions - What Card Is The Best? comparing transactions in Singapore.
Overseas Transaction - which CC to use? HSBC rate was among the highest for US and SG transactions.

Tell you what, you go do cash withdrawal with your HSBC ATM card and also pay with your MBB Petronas Card and then report here back the exchange rate comparison please.

Thanks for letting us know that we can get discount (not rebate right?) with MBB cards for Universal Studios and at the Zoo in Singapore. However, I have not been checking the promos for Universal Studios lately but the last time I was there, they will offering some promotion with MasterCard.