Depends on how much money you have to burn ;) There's also a crop factor issue when using digital backs, since they aren't the same size as the original film.

Depends on how much money you have to burn ;) There's also a crop factor issue when using digital backs, since they aren't the same size as the original film. If you have a lot of money to burn, the latest gen digital backs are close enough to 6x4.5 that the crop factor is fairly insignificant. Older digital backs aren't even close, so you're shooting a substantial crop from the original intended image. There is no such thing as a 6x6 sensor, unfortunately.