@Sel - It's DE Sidious, not RotS Legends Sidious. Dark Empire claims twice that the Emperor's powers were "ever-expanding", and the Dark Empire Endnotes say that he continually grows more powerful. The Dark Empire Sourcebook goes on to say that his Force skills have increased significantly since RotJ.
It's fair to say that DE Sidious is substantially above RotS Legends Sidious, whose Lightning feats of incinerating Sith wyrms, being comparably powerful to hurricane winds, wiping out small armies, and actually overpowering Yoda's Force defenses supersede anything he's done in Canon. There's also him in Y: DR generating Weather Storms across the galaxy with the onset of his mere hologram. That's pretty insane.
Honestly, Canon Talzin doesn't really compare to DE Sidious.