dcollins said:
Indeed, the only +5 limit in the rulebooks is to the enhancement modifier itself (DMG p. 179, 183).
As an aside: Why not keep it simple, skip the house rule, and just play this one by the books? Seems to work for most DMs.
When they start facing foes with DR, they'll wish they had that +4 rather than the Keen and Icy Burst enchantments.
It's really a trade off. One I seem to consider heavily when creating NPCs. One I considered much more when trying to decide if my Paladin needed a +2 (and Frost) or a +1 and Holy. I took the later and, at times, regreted it. This example comes from lower levels but does tend to show up later in different forms.
Now, what I would consider house ruling is that when they cast, say,
Greater Magic Weapon, it comes up against the +10 limit. Meaning, if they have Keen, Holy, Flaming, and Vorpel on their weapon (coming to +9 in extras) and have a +1 enchantment bonus, the spell will either not funtion past +1 or surpress the other effects (making them inactive), from the smallest to the largest (keen first, Vorpel last) until the spell takes up the enchantment bonus desired.
This prevents the work around some players will try to use. Besides, I don't think the spell is really stong enough to push a weapon up to an effective +14, regardless of the length of time.
Of course, I wouldn't tell my players about this one up front. After all, how often does this come up in normal lives? It's not going to be common knowledge. Remind them that you're thinking of them with enchantments that suddenly shut off.