It’s worth noting that bond prices tend to move before the RBA cuts rates.

In fact, one of the things that are a decent predictor of future rate moves are the bond markets. The lower rates become priced in before they happen. So if you thought you could buy bonds, then when the RBA cuts rates, they’d go up in price, then it just doesn’t work that way.

As a place for holding cash short-med term it makes sense. But I reckon you’d likely find that a mortgage offset is superior for two reasons: the rate is likely to be higher, plus the return is tax-free (assuming it’s your residence not an investment property).

You might get fortunate and get gains from whatever has not been priced into bond markets already, but that would probably be more luck than anything.

I like the question.
I think tax will eat most of the gain on the bonds compared to no tax on the saving you make on the offset.
But just the higher rate 2027 maturity bond could come out ahead if mortgage rates come down a fair bit.
Many assumptions in spreadsheet below, tax 30%, 6% starting mortgage rate, buying multiple of $100 face value on commsec price today. Getting both coupons on GSBG26 (Oct-25 and Apr-26). 11 months of mortgage savings in 1st year. Please correct me if I’ve missed something.

                     GSBG26         GSBG27     Offset no cut       Offset cut

Rate 4.25% 4.75% 6% 5%
Maturity 21/04/2026 21/04/2027
Buy price $100.85 $103.16
#bought 0.99 0.97
interest -26 $4.25 $4.75 $5.50 $4.58
interest -27 $0 $4.75 $6.00 $5.00
tax $1.28 $2.85
sale $99.16 $96.94 $100.00 $100.00
gain $3.81 $9.71 $11.50 $9.58