I read about some wind tunnel tests that were conducted back in the 1930s by NACA, as I recall, of both swept back and swept forward wings. Swept forward wings were found to have a slightly reduced induced drag, but not enough to offset the structural problems, or we would see far more airplanes with swept forward wings. The tests were done at low Mach numbers, and the investigator concluded that both sweepback and sweepforward had no future, but this was long before the supersonic era.