It seems that you are equating negative size to linear dimension. Negative size is a matter of square inches of negative. 4X5 would twenty inches square, 5X7 would be 35 inches square (almost twice as large as 4X5), 8X10 would be 80 inches square (four times as much as 4X5). All things being equal a 8X10 negative could be printed four times as large as a 4X5 negative and maintain the same print quality.
Originally Posted by Tom Stanworth
Color materials will print larger then black and white materials when equivalent negative size exists. Just the nature of the beast.