Gunmans would be speed plus power, following the "best defense is good offense" principle. They'd really not have much finesse at all.
I'm not sure which would be defense and which would be finesse, but I know I want the remaining two power slots to be between the Arbalester and the Sniper.
From there, who knows.
For the Back class, I got speed and power as the assassin, with sped and defense as the ninja. Power and finesse would be the reaper (Power for Back basically means 'lethality'), but that's about all I've got.