my cents worth...
you should hold on to your hdb and rent it out for passive income... there's no better income then to have a passive income which will generate revenue for you even when you are not working! when you rent it out, your tenants are actually paying the rent for you and still have some cash balance from the rental while you only have to worry the instalment for your pte apt. think it the other way.. your tenant is also subsidising partially your instalment for your apt as well.
hdb loan is the best singapore housing loan as the interest rate is fixed at 2.6% or rather 0.1% pegged on cpf interest rate. as long as cpf interest remains the same the interest will be forever... why bothers to go for early redemption to your hdb?
if you wanna save more interest, why not pay more for your pte apt instead and hopefully redeem your apt the soonest as the interest rate is more prone to the market situation and sentiment.
Most successful property investors if you realised had been renting their property out for long term investment instead of basing on flipping/buying&selling... As quoted by donald thrump; the most hatred and yet one of the most successful biz man: 'The longer you hold, the more you make'.
Hope this one helps!!!
Pet