Donald Qualls
Subscriber
6x7 is not 5/8 the film area of 4x5. Not even close.
Based on those dimensions you quoted 6x7 gives around 30% of the area captured by 4x5.
Woops, you're right; it's about 5/8 the linear dimension. If we deduct the film holder masking for 4x5, we get about 98x120 mm, so 56x70 is exactly 1/3 the area. Your mileage may vary depending on exact gate dimensions (which vary between 6x7 cameras and roll holders) or exact film holder masking (which varies less, but still some, between brands of film holder).