The nine-storey Optimum building is 90% let. : A core-plus fund managed by Conren Land has acquired the 17,000sqm Optimum office building in Vienna from Commerz Real for €55m. The building, at Dresdner Straße 81-85 / Traisengasse 1, has been in the Commerz Real open-ended real estate fund HausInvest since its completion in 2000.