
Scott Wilhelm |
It's wielded as if it were a scimitat, but I don't think that means it is a scimitar or any other kind of weapon.
Flame Blade looks to me like it's a spell that grants you the ability to make Melee Touch Attacks that inflict Fire Damage.
I agree with Melkiador: I don't think it benefits from Size Increases of any kind. I think that if you were wielding a Flame Blade, then you cast Enlarge Person on yourself, the 'Blade would still be 3' long as per the spell description. It would still inflict 1d8 +1/two caster levels, and you would not suffer a penalty for wielding an inappropriately sized weapon.

SheepishEidolon |

If you want a blade of fire as your main trick, kinetic knight is an alternative. Means you get +1d6 every two levels instead of just +1. And you can use it directly, no need to cast something before combat (or worse: during combat).
Anyway, if you want more damage from flame blade, Empower Spell gives you +50%. Further, you could use more metamagic (such as Elemental Spell to switch damage type), increase your caster level (for a minor damage boost) or pick up the dedicated feat Flame Blade Dervish.

Mysterious Stranger |

Flame Blade specifies in the description that it is immaterial and because of that it does not add your strength bonus to damage. Lead Blades extra damage from lead blade is due to the increase of the momentum and density of the weapon. Since Flame Blade is immaterial how can you increase the density? If momentum increases the damage from Flame Blade, you should be getting your strength bonus to the damage it does. These spells do not interact at all based on the description