Uh, wouldn't the polypore end up being cheaper than fire surge since you don't have to pay for runes, even with the rune-saving effect of the SoL? Either way, SoL is better at Glacors because fire surge gets the damage bonus of fire v. ice. Unless you were talking about merely equipping the PPS and not using the special spell and instead casting fire surge with the PPS, in which case the PPS wouldn't degrade. But if it's only a +3 mage difference as you said, I'd personally bring the SoL for the rune-saving effect.