Well the main consideration is that the current price of S5pro price has drop very much compare to few years ago. It is much affordable now.
D80 in reality cannot be compare with S5pro. you should use D200 to compare. Guess some brother said, S5pro is slightly bigger than D80 and it is consider as a full body system.
Given a choice i will go for S5pro. you get better satisfaction with it.
I am currently using it with a Nikon SB800 flash no problem, it is working well.
Regards