I'm a huge Forrest fan, I think the only way Forrest can win is by decision. He could win the later rounds as Rashad may gas out.
However, I think it's more likely that Rashad knocks Forrest out. Rashad has more powerful and faster hands than Forrest. Pretty much going to be the same story as when Rashad fought Chuck, but Rashad will have to take the risk of getting inside Forrests range more because of Forrest's height and reach advantage.
Rashad via KO or TKO in my eyes.
Always Supporting Fighters That Fight to Finish or be Finished