udalrich said:
I can actually see logic to support both sides of the argument. Bane increases the "normal enhancement bonus". The weapon in question has two enhancement bonus: the +1 bonus from being crafted as a magic weapon and the +5 bonus from GMW. Unless "normal" is a game term whose definition I missed, you have to figure out which one Bane affects. Essentially, you have a +5/+1 weapon, where the +1 doesn't normally matter so we tend to forget about it.
You can either assume that "normal" is the one permanently attached to the weapon (+1), in which case Bane and GMW don't stack (you get a +5/+3 weapon). Or you can assume that "normal" is the one that would apply if you used the weapon now (+5), in which case they do stack (+7/+1). If the party wizard normally casts GMW on it first thing in the morning, you could even argue that the +5 bonus is applicable, because it's the bonus that is normally used with the weapon. (I doubt the last argument would work with many GMs, including me.)
There's certainly a reasonable argument that can be made for increasing the +1, since both the +1 and Bane are permanent effects, so it's reasonable to assume that one permanent effect modifies the other permanent effect. Personally, I would lean toward this interpretation, but I think the rules are ambiguous and require a house rule to clarify it.
I agree it's a reasonable argument, but ultimately, I don't think it holds much water. It's not that the weapon has multiple enhancement bonuses, it has only one enhancement bonus. It has multiple effects which grant an enhancement bonus, and only the strongest effect is at relevant. If the enhancement bonus of a weapon is +5, then that's it's enhancement bonus: at that moment, it doesn't make a difference what was, what might be or what will be. It has an enhancement bonus of +5. Bane improves that enhancement bonus by two - whereever it happens to come from. Why is it only improving your "normal" enhancement bonus? Since it's not improving the resultant enhancement bonus (it only stacks "once").
There's absolutely no problem, balance or otherwise, with that ruling. It's simple, and consistent, and doesn't require you to keep track of "multiple" enhancement bonuses (what happens if permanency comes into play? Is that "normal"?)
There's exactly two issues that it doesn't address, and that's whether multiple banes stack, which you can either resolve by simply not allowing multiple bane enchantments at all, or by allowing them to stack, or by considering them "the same source", so they don't stack. I adhere to the last interpretation, since it doesn't encourage "pile it on" play. Can you imagine the poor Hellhound otherwise vs. a Evil Outsider bane, Lawful Outsider bane, Fire Outsider bane, frost weapon? Heck, that sounds so funny I might just allow it for kicks. In a one-shot anyway! I mean, that way you could make a +11 non-epic weapon
The second issue is that of epic damage reduction. Epic Damage reduction applies literally to all attacks with weapons of +5 or less enhancement bonus. That means that bane might circumvent it. You either accept that (fine by me) or you don't, but do allow bane to exceed +5 enhancement bonus (which follows the rules only in spirit, but not to the letter), or you just don't allow bane to exceed +5 enh. bonus - the most restrictive interpretation, which, considering the section on magic weapons in which bane is defined, which says that a weapons enhancement bonus can't exceed +5, is also consistent.
I'd be inclined to leave epic damage reduction in epic territory - i.e. uncircumventable by mortal magic

. But I don't really care either way, as I'm unlikely to encounter a situation in which it matters. An it only really matters at level 15+, in practice, since you either need a caster of 16th level to create at least a +4 weapon via GMW, or enough money to spend on a +4, bane weapon. Is it really that important, at that point? Are weapons which only overcome damage reduction versus a very specific epic opponent really that interesting?