I think Saad would ultimately get to him late. I question if Ward has enough firepower to deter Saad long term, and in Saad we're talking a different beast than Kov, Kessler, Froch, and AA.
Over 15, I take Saad. Froch came on pretty strong in the late rounds. Saad, being level above him - and having three extra rounds - would turn the only rounds Froch won to winning by KO, IMO. Ward would probably take it over 12.
No matter how far Ward is ahead, Saad could literally turn the fight in his favor with one punch. So for that reason, I'd pick MSM
As others said I'll pick Ward by decision if it goes 12 rounds. I would give Saad a better chance if the fight went 15.
As a LHW, Ward really lost to Kova (who was at the tail end of his prime) in their 1st fight IMO, and then had to open himself up to a lot of punishment in order to wear him down in the rematch. I'd favor Saad here.
Kovalev may not have the intangibles or toughness that Saad had, but he's so much better technically than Matt that it's untrue. Not even worth comparing IMO.