Welcome to Librarium Online!
I really like the idea of this item and the cool conversion potential of it, but do people think it is really worth it?
Combine it with Red Fury and Infinite Hatred and you have a fair chance of taking even a steam tank out in one stroke? The problem is you are only Strength 5.
In large games (3000pts+) then it is worth it. The cost is just too high for standard points games. The example you provided above costs 370 points. I can have a powerfull spell-casting Vampire Lord which can support your army better (or can even deal more damage with Forbidden Lore) than an offensive close-combat Lord.
Wight Kings with a Great Weapon/Sword of Kings (or the Black Axe of Krell) are cheaper and can act similarly with Killing Blow. If you have the points you can give him Frost Blade.
Besides, who charges a non-Chaos character (not Monster!) into a Steam Tank?
My 2 cents.
When life gives you anything, charge it with Genestealers.
Alarm clock? Genestealers.
Your boss? Genestealers.
The rednecks that cut in front of me at Wal-mart like I didn't have anything better to do than stand in line? Genestealers.
The best time to take a frost blade is against high toughness/multiple wound armies..... Ogres!!!!
The combat res bonus (loses remaining wounds....) is phenomenal! eg - 5 attacks gets 4 hits gets 3 wounds (gets 3 more attacks gets 2 hits gets one wound) equals 4 wounds equals 4 dead ogres equals a combat res of 12!!!! Just from the Vamp!
Plus any bonus kills from the unit he is in and that's a big batch of fleeing ogres. If they play BFB Ogres (18+ iron guts + butcher + Tyrant.....)
Its one of those weapons that you take if the enemy loves their multi-wound models. Just give the count the Frostblade, avatar of death, and wings and send him into the closes Treeman/Treekin/Ogre/Hero/Dragon/Stank/etc.
40K armies: Tyranids (2001), Space Wolves (2008), Sisters of Battle (2011)
Current Rep: 1337