I'm well aware of the raw Sorcerer capabilities of Vitiate, not to mention his incredibly hacked power levels - but here are some of Sidious' exploits:
Killing thousands of Republic troops with a standard Sith Lightning (EaW) that lit up the surface a planet.
Vaporizing traitors (Darth Vader and the Ghost Prison part 5) with standard Sith lightning.
Bending a lightsaber blade with standard Sith lightning (RoTs).
Using Force illusion to hide an Imperial Star Destroyer from the entire population of Coruscation (Shadows of the Empire, IIRC?).
Subjugating hundreds of armed Bothan traitors with mind control (EaW) while killing a few hundred more with his lightsaber and Force lightning.
Insta-killing three Jedi Masters (including Kit Fisto, who was demonstrated as being capable of defeating General Grevious in combat [TCW]), all of which were some of the best swordsman of the Jedi council (ROTS).
Killing three Jedi instantly and causing an awed Jedi to kill the fourth to save himself (Dark Times, A Spark Remains, Part 3).
Creating a Force storm that darkened Coruscant, momentarily disrupting Yoda's ability to use the Force in battle, vaporizing a Sith-spawn that he created with standard Sith lightning (Visionaries).
Overpowering the venerable Master Yoda.
After proving that he could have killed Maul and Opress (two Sith who previously slaughtered scores of Jedi in a novel I can't recall; before conquering the Mandalorians, Maul himself killing the Mandalore and taking the Darksaber [TCW]; not to mention Maul is proven as slightly above TCW Obi-wan and his former master Qui Gon Jinn [TCW][TPM]) with TK alone. Then Sidious toys with them for a while in a lightsaber duel, wielding two lightsabers no less - before killing Opress while laughing and then tooling Maul and torturing him with standard Sith lightning.
Creating a blast-wave that nearly turned a helpless Plagueis - whilst making everything in the room fly around along with the palpable currents of dark side energy - into a charred husk (DP novel).
Slaughtering hundreds of various military grade battle droids along side Plagueis early in his training - before growing tenfold in power (DP Novel).
Performing the ritual that tipped the balance of the Force galaxy wide in the dark side's favor, effectively scaring the midi-chlorians into immaculately conceiving the Force vergence that would be known as Anakin (DP novel).
Has more statements as being the most powerful Sith in history than any Sith before or after him (EU canon).
Subjugating and Force draining Byss, summoning Force storms that consumed the entire Rebel Fleet at once, increasing the power of his subjects, shrugging off several tons of steel that Leia threw on him before effortlessly disintegrating her lightsaber with a gesture, tearing apart a Jedi's environment suit that could allow him to survive in space without food or water for weeks with a lightning strike (DE, DE II, Empire's End, and the Sourcebooks) while in a weakened state.
The burst of his standard Sith lightning instantly kills Galen Marek, a Grey Jedi who could move a star destroyer (TFU).
Is the product the Rule of Two, inheriting the sum of thousands of years of progressively more capable Sith; starting with Bane - one of the most powerful Sith of all time.
As of RoTs he's already half of NJO Luke [Empire of Dreams documentary by Lucas, and another statement by Lucas on Luke's equal potential to Anakin that I could dig up]
The list goes on. I think you get the point.