The first fight with Gluttony, Scar deflected his attack and blew up his head. Gluttony then struck him in the chest, badly wounding him, then Scar blew off Gluttony's arm. After a skirmish, Scar was forced to flee. The second battle with Gluttony, Scar was knocked through a wall and fell into Greed's old prison. Gluttony was clearly superior in that fight - but yeah, Scar was still wounded in it from his first fight with Gluttony. Last we saw, Scar is still recovering from his wounds.
I would say that Scar's faster, but not by a whole lot. Gluttony's obviously far more durable, though, and stronger.
As for who dies, I'm pretty sure it will not be Mustang/Hawkeye. He seems to be purposefully ignoring the situation, in order to become Fuhrer and change the world. If Armstrong is legitimate, then he is likely to become the next victim; Or the booklady, who the Sins have to know worked for Hughes. The idea of Winry being killed so the Philosopher's Stone would undoubtedly be used to resurrect her is very interesting, but I couldn't see it being done until the mid-40's+ in this series...