Singapore’s luxury real estate market is likely to be hardest hit by the government’s most-recent property curbs, with sales forecast to fall between 30 and 40 percent in the next two quarters. Overseas buyers, who accounted for one-third of luxury property deals last year, may balk after the stamp duty on foreigners was raised to 20 percent from 15 percent. “More foreign buyers have been eyeing Singapore’s luxury homes for the past year, but they may now take a back seat,” said Christine Li, a senior director and head of research for Singapore at Cushman & Wakefield Inc