Other areas you can consider but might not meet your expectation in IRR might be the Singapore Saving Bond for its safety.
Currently it is not possible to buy SSBs using SRS funds. There's some discussion about lifting that restriction, but I wouldn't bet on it.
However, Singapore government bonds can be purchased using SRS funds. (It's a manual, paper-based process that requires stopping by your SRS custodian's branch, and most bank employees would struggle to dig out the right form, but it's possible. Call ahead so at least you don't have to wait for them to dig out the right form.) There are no more Singapore government bond auctions in 2017, but in 2018 there's a 5 year auction in January and a 10 year auction in April. There might also be a special auction in March for an interesting tenor. The 30 year (February) is not a good fit for SRS accounts. I personally wouldn't go longer than 10.
Bonds are auctioned in $1,000 face value increments. You won't be able to sweep every dollar and penny from a SRS into a bond, but you can get fairly close. There are absolutely no fees or charges to buy Singapore government bonds at initial auction and to hold them to maturity. (SSBs have a $2 purchase charge and a $2 redemption charge. SGSs do not.)
If market interest rates hold steady from now until the auctions then you'll probably get about 2.15% on the 10 year, maybe 2.20% (noncompetitive bid assumed, which is what individual investors should do). The 5 year would be around 1.75% or 1.80%. That's not 3% to 4%, but it's the #1 safest Singapore dollar investment.