Wow, thank you for all the great info! You are a Zealot encyclopedia!!

If I'm not investing my tempo to boost strikes then is Rubato Bard really adding enough? The damage cycle you described is fantastic and my actions are all spoken for, so pre-combat buffs or a single round to get big might be the best thing to look for in a second class.

Alchemist would provide Enlarge (and an extra hand to hold a shield), high reflex save, and Heroism at level 7. Not as efficient as Bard for free action boosts but it could add similar numbers.

Or Psion (Egoist) would give me Metamorphosis, which is 6 minutes of +2 size categories (+4 STR, boost the greatsword 2D6) as well as a list of handy stuff like DR, fast healing, natural armor, or mobility. I could use a bonus feat on Improved Metamorphosis, which I believe would let me boost my strength up +8 total. I lose my reflex save, which might be a bad idea, but for pure damage I don't see a better way to buff myself before charging in and starting the Zenith Strike cycle.

Rogue or Ninja adds +3D6 sneak attack, skills, and keeps the reflex save, but it's not going to scale as well as a caster. Soulknife (Gifted Blade) has the reflex save and Expansion, which can eat up all my PP to grow two sizes or at least stay large for a long time. The downside is that all those Blade Skills look mostly useless for a pure strength greatsword guy.