I'll do it.
Here we go, without Improved Metamagic:
12th-Level Spell - Vampiric Touch [Maximize, Empower x3]
60 (10*6, Maximize) + (3.5*10/2)*3 = 112 damage
OR (since Vampiric Touch isn't the only spell there):
13th-Level Spell - Horrid Wilting [Maximize, Empower]
200 (25*8, Maximize) + (4.5*25/2)*1 = 256 damage
OR (for those of you who will complain about me combining feats):
13th-Level Spell - Vampiric Touch [Empower x5]
35 (3.5*10) + (3.5*10/2)*5 = 122 damage
OR (again with the other spell):
12th-Level Spell - Horrid Wilting [Empower x2]
112 (4.5*25) + (4.5*25/2)*2 = 224 damage
With the above examples, no longer using Improved Metamagic, Wizard STILL would have won the fight! How? Use the Horrid Wilting instead of the Vampiric Touch as the partial action in Round 1! Even with a successful save, any number of other spells could have killed Fighter instantly the next round!
So, now that I have stopped using a Deity and Orcus and Improved Metamagic in my exmaples, yet STILL shown that it does a ridiculous amount of damage, NOW do you believe me?
I'm not debating what the rules say about stacking being allowed, I saying IT'S BROKEN!