As for a step down, it will depend on how big a jump you are comfortable with. Jumping to the Tag is a bigger jump than the Panic or the Tribal Fire. For THS I can see the Tag being a good step down.
However, for conditions where you don't want as big a jump, having either the Panic or Tribal Fire (Panic being a tad smoother) might be better. Then from there you can go down again to the Tag and/or Ascent Apex.
As for a step up, are you looking for the same shape but stronger, or a ball to start with then transition to the Redline? Early reports have the Redline being a bit more angular than expected. So same shape but stronger could be the Remix or, with an adjustment of the cover, the Vengeance. If you want a ball to start with, either the Covert Revolt/Revolt Havoc (stronger) or the Forza (relatively same strength as Redline) could be used.
A lot of ball selection up/down depends a lot on how you plan to attack the shot in question. Once you have a plan, selecting a ball should be easier.