Having the Infinite Theory and the Outlaw (the ball that was replaced by the Disturbed), there really isn't much that you can do in-between. Both balls handle medium-heavy oil and basically the hybrid will have higher flare potential from the asymmetric core/cover combo. Unless you are drilling a second Infinite or Disturbed with a different layout, don't bother. The Infinite already is a step up from the Disturbed but below the heavy oil balls from both companies.
Going above the Infinite Theory, you could easily go with a Defiant or Sync. Both handle heavy oil well. I bought a Defiant shortly after it came out and I love how it performs. It works well for all styles, has a great core, easy to tweak layouts, and it provides a reliable arc motion that is consistent. The Sync is similar, but will give you a couple of boards more and a similar motion.
I would focus on the gap between the Disturbed and Tropical Heat Hybrid. In that spot, you could easily fill in a HyRoad or CrossRoad.
