2 for you in my regular based army.
Dreadlord with Caledors bane (so str7 on the charge) potion of strength (+3 str 1 round of combat mine or yours - one use only), Pendant on Dragon, heavy armour, shield.
But the once I'm talking about is my Razor Assassin - 3 attacks +1 handweapon + d3, Killing blow (and when fully maxed out although this is rare he's also got manbane).
TBH I'd probably take out less then 3. My rought math hammer has it at:
Dragon rider = 3 wounds at 6+AS, 5+ ward so 2 dead around.
Dragon = 3 wounds at 5+AS, 5+ ward, 2 go to ward so 1-2 dead
Assassin = 6 attacks on average, 4.5 hit, 3 or so wound, 3+AS put 1 wound at 6+. Then again I seem to roll very lucky with this guy (got 2 kB on manfred with 4 attacks and 1 on my opponents regen wright king killing both! haha).
*keep in mind the assassin is in a unit of Black Guard usually buffed with KB from the couldron as well.