That's a nice hack. Can you explain what you mean by "Interest earned in your Retirement Account is not counted toward this particular limit"?
Sure. Let's assume that you top up your newly formed Retirement Account to the Enhanced Retirement Sum within the calendar month that you celebrate your 55th birthday. Your Retirement Account then earns interest starting from the first day of the following month. Which is why it's ideal to get this top up
credited within the tail end but not after your 55th birthday month, so the top up can start earning interest as soon as possible. This interest is paid/credited, of course. But the interest is not factored into determining whether you can top up to every new, higher Enhanced Retirement Sum. Under current rules, every time the government raises the ERS, you're welcome to top up your principal to the new, higher ERS. Interest is above and beyond these ERS limits.
That is assuming that one is still working between 65-70 before the payouts start at 70.
No, that's not a given. You're welcome to defer payouts to age 70 and to draw from your other assets before age 70. In terms of maximizing the longevity insurance benefits of CPF LIFE, that'd be the smart play. Your decision whether and when to stop working for income is a separate decision, really. And you don't need an annuity to "bridge" to a specific age, such as age 70. That you can do on your own, using traditional savings, appropriately paced withdrawals, and prudent investing, some of which might involve other CPF deposits. For example, if you don't have other CPF contributions (from work for example), you're allowed to deposit the CPF Annual Limit each year. That's an "all three" top up, and your top up will be allocated across your MediSave Account, Ordinary Account, and Special Account according to the standard allocation rules for your age.
The dilemma that I'm having is should I go the SRS annuity route that gives tax breaks, but also undetermined and unguaranteed projected returns? Or do something else.
If you find that a couple's CPF LIFE monthly payouts (age 70 payout start, Escalating Plan, repeated ERS top ups starting at age 55) don't provide enough longevity insurance for your needs, then you could go take a look at a SRS-funded insurer guaranteed single premium life annuity, such as Manulife's. Or an overseas life annuity in another major currency from a high quality insurer, which is a bit exotic to be sure, but the basic idea is that it would defend against a weird, severe, sudden devaluation in the Singapore dollar. I'm certainly not predicting any such Singapore dollar weirdness, but I can see some value in a little life annuity diversification that way.
With regards to refund of the CPF OA monies used for housing, the issue is that there is no tax break for it so although I'm gaining 2.5% interest, I'm losing out on tax breaks.
A Supplementary Retirement Scheme (SRS) account is a reasonable way to funnel dollars into a Singapore dollar denominated life annuity, again provided a pair of super-ERS-level/age 70 payout start CPF LIFE monthly payout streams is something you consider an inadequate amount of longevity insurance.