Player Researched Spell / Celestial Aspect (Avoral)

[reiella]

One of my players has come up with a spell idea (prodded by some in-world requirements for advancement as a wizard) and I'm toying around the balance issues with the spell.

It's based roughly around Fiendform in it's design, and just curious about opinions/takes on it. And if it is "too much" what to suggest to the player after the character fails the research (I'm a RB ).

Celestial Aspect (Avoral)
Transmutation
Sor/Wiz 7

Casting Time: 1 full-round
Range: Touch
Target: Creature Touched
Saving Throw: Fort (negates)
Spell Resistance: Yes
Duration: 1 hr/lvl
Components: V,S,M

Description: As polymorph other except the target creature is transformed into an Avoral Celestial and may use supernatural and spell-like (but not exceptional) abilities of the Avoral. The target's type changes to outsider (good) and spells and effects that harm or ward good outsiders affect the target. A spell that would banish the target to their home plane ends this spell and leaves the target staggered for 1 round per caster level, but does not send the target to another plane.

Material Component: Tourmaline worth at least 750 gp.

At a glance, it's pretty similiar to Fiendform in its operation (7th level spell, transforms into a creature summonable by a Summon Monster XII) so I'm ok with that part . The "but not exceptional" is redundant, as the Avoral doesn't have any exceptional abilities of note, so I don't consider it too much.

Right now, I'm thinking it may be a bit overpowered, but would be ok if shoveled up to 8th level or duration reduced to 1min/lvl.

[ Quick Reminder, 3.0 Rule Base ]

Add/ Edit DOH

Oh yea, forgot to mention, I'm not too willing to add an xp cost to the spell (as I've done away with itemized xp awards in my campaign, just tell the party when the level up ).