To find the length of diagonal CF, we can use the distance formula in three dimensions.
The coordinates of point C are (0, 0, 0) and the coordinates of point F are (5, 6, 4).
Thus the length of diagonal CF = sqrt((5-0)^2 + (6-0)^2 + (4-0)^2)
= sqrt(25 + 36 + 16)
= sqrt(77)
= 8.77
Therefore, the length of the diagonal CF is 8.77, which is answer choice (B).