Anyone speaking digitalese should have their mouth washed out with soap before posting again. 6x9 is
a different shape than 4x5, so an exact ratio makes no sense anyway. Being a smaller area of film potentially requiring more enlargement means you will want very sharp lenses for high quality work.
I personally often use a Fuji 180 with 6x9 exposures and it is a superb performer. It has about the same "feel" as when shooting a 240 on 4x5, but again, a little more linear or panoramic rectangle.