Legin,
you are dead right.

It is not as if the Struct. Eng. is going to say that the RSJ must be
7.92837465 inches deep and 4.847294756 inches high. It is going to be
from stock so put in a big fat one.

What is above the lintel anyway. Apparently if you opening is 7 Feet
then the lintel has to support the weight of material in an equilateral
triangle of 7 Foot sides and the wall thickness.

Chris.