Thanks for the input Anthony, and your experience is interesting and on
point.

From all the input received here, I now have no doubt that I can span 20
feet easily, using #2 southern pine 2 X 12 beams , on 16 inch
centers.

I remain curious if anyone can still answer these remaining questions that
were in my original post:

--------------------------------------------------


Is #2 visually graded, the most common lumber found in lumber yards ?

Which would be better, 2 x 10 on 12 inch centers or 2 x 12 on
16 inch centers ?? It seems that the latter may be a bit cheaper, but price
isn't the primary concern.


What happens if you use a 2 X 12 beam, but put them on 24 inch centers
instead of 16 inch?? Do you simply get more deflection, and less load
capacity ?