Nice idea, but I do have a couple of nitpicks:
Elemental damage doesn't remove Stoneskin, it just goes right through it. The sword you have outlined would be a tremendous boon to Wizard Slayers (who currently need all the help they can get), but it's not quite justified. For instance, Red Dragon Dust would be far more likely to confer
Fire Resistance than
Magic Resistance, and the sword would probably cast a 10D6 Fireball instead of Breach.
Hey.....how come we don't have any suggestions from Dundee on here yet? Hmm. Tell you what, I'll bait him.
Hey, Dundee!! What do you think you would get if Cromwell/Cespenar combined:
- Robe of Vecna
- Ring of Gaxx
- Book of Kaza
- Lich's Tooth
- Halberd+2, Duskblade (optional)
- Skull of the Lich (optional)