5LA / 3HD Loredrake Tome Dragon / Rainbow Servant 10 / Arcane X
Lose Knowledge domain from Loredrake
Versatile Spellcaster (Already know 3rd level div/conj spells, no need for heighten...)
Rainbow Servant interpreted as 10/10 casting
LA-Buyoff 3LA Allowed
Spontaneous all Divination, Conjuration on the sorcerer list
Cleric List access
Making it 20/20 caster
Spontaneous access to around 200? spells of conjuration and divination is pretty nice. Telepathy. Next age category going another 3HD for 2 CL gets you to +1 free metamagic & rapid metamagic on the Tome Dragon as well (19/20). Like a Versatile Spellcaster Warmage, can start belting out higher level Conj/Div spells ahead of the curve.
Steel Dragon is a much quicker route to the cleric list, though you end up eating 3CL since you would want to avoid Loredrake, no 9's for shame.
Could use age abuse to reach higher power levels, as discussed in the other dragon threads.
If the Knows Conj/Div spells was interpreted as added to any class they posses, could only squeeze in 15 levels of Warmage casting levels.
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For completeness
Hex Dragons
Wyrmling 4LA / 4HD, No CL
Very Young 5LA / 7HD , Caster Level 1st
Knows all Enchantment & Necromancy Spells on the Sorcerer list
Spontaneous, yes. Effective, no.