Khristos said:
My high level fighter has a pair of adamantine +4 defending shortswords....our wizard gains 1 more level and I will have +4 defending vorpal shortswords in short order....
I don't think you can put vorpal on piercing weapons. This might have been errata'ed, however.
granted another evil campaign so I lost 2 lvls of BAB thanks to lvl 13 going to rogue and lvl 14 to assassin but the opening full attack sequence with 2 dragonbile coated blades usually means 3d6 strength damage if a creature isnt immune to poison as I am bound to hit somewhere in my 5 primary and 3 offhand attacks... blessed boots of haste
(Fighter 16 Rogue: 1 Assassin: 1) Oh and with the magic of quickdraw it usually also means 8 possible failed DC:14 saves vs fortitude which leads to the poor victim dying outright.
Sure, in your case, the two weapons are very good as a delivery system for the poison and death attacks (though that save is not very hard to make at those levels since nearly every monster of CR 18 or so has ungodly fortitude saves (outright immunity to poison in many cases) and adventurer-types will always have immunity to poison through Heroes' Feast), but unless I'm missing something, that's not very good at damage dealing. But you already said that.
In fact, at first glance (I'm probably missing something), it seems quite underpowered, overall. The sneak attack is only 1d6. Also, I'm not 100% certain about this, but I think you need to study your target for 3 rounds before every death attack, so I think only the first one in each full attack could be a death attack. And the poison is very expensive and only good for one attack per dose, not to mention the unlikelihood of affecting anything (CR 18-20 monsters in the MM: Nightshade - immune, Dragons - immune, Balor - immune, Pit Fiend - immune, Tarrasque - Immune). Now, with the vorpal thing, you're on to something, but then we're back to two weapon style being only a vehicle for delivery of many special attacks.
But I'm probably missing something here... :\
Also a pair of +5 weapons probably isnt much if you had coin appropriate per the DMG for an 18th lvl character (once one of the wizards hit midway 18 the values will shoot up to +10)
A pair of +5 weapons is not. A pair of +10 weapons, however, is 400k out of the expected 440k gp a character of that level should have.