Rhun
First Post
Spells don't follow crafting limitations as far as I know.
GMW should work just fine. But there are a couple major drawbacks to your strategy. First and foremost is that your weapon is very vulnerable to dispel magic. Any area dispel will hit your weapon as well as you. As this should be a frequent tactic of enemies at your level, its a big thing to consider.
It is NOT a crafting limitation: "A single weapon cannot have a modified bonus (enhancement bonus plus special ability bonus equivalent) higher than +10." There is no mention of crafting anywhere in that sentence. It is clearly spelled out that a single weapon cannot be higher than +10.
With that said, it honestly isn't going to come up a whole lot, except maybe in very high-level games. If your PC has a +5 vorpal sword (+10 modified) and somebody casts a +5 GMW on it, it is still a +5 vorpal sword (since only the highest enhancement bonus applies, and they do not stack).