Act of Treason at instant speed is amazing on defense, IMO. Stealing one of the opponent's creatures and 2 for 1'ing them is kind of a big deal. Assault Strobe is one that goes from being barely passable to decent when it can be cast after blockers are declared. Ponder, Serum Visions and Preordain become Brainstorm, Mind Spring becomes the greatest opponent's end-step spell ever, that kind of thing.
Just about any discard spell is a big deal at instant speed; a Raven's Crime during the opponent's draw step will keep an opponent from recovering from a Hymn to Tourach or two, y'know.
Besides that, the fact that Hypersonic has Haste is generally enough to be useful on his own not to mention the instant-sorcery bonus. They're both useful, and running both isn't necessarily a bad option. I also like either Niv-Mizzet for that kind of thing, as well.