Bash vs Slam

[Algustus]

Hey folks, I'm playing a low level warrior and recently picked up a shield of the Slain Unicorn, which gives me shield armor and an off hand piercing attack but no bash. I like bashing spellcasters to interrupt their casting. My warrior is a barbarian so slam attacks are an option. How does slam compare to bash for interrupting? Does the increased damage of a shield bash also increase the chance to interrupt a caster as compared to a slam attack?