[3.5] Gem Dragon Familiars?

[Extra Anchovies]

Hey all!
I'm currently planning out a Duskblade for a future game and want to eventually gain a familiar who will fight next to me. The dragon familiars look really appealing, but I've never really been too keen on the chromatic and metallic dragons; the gem dragons are much more to my liking. My plan is to take Obtain Familiar and Dragon Familiar at 6th and 9th or 9th and 12th levels, respectively (I'll be a human, so I'll have Knowledge Devotion, Arcane Disciple {for that tasty, tasty Time domain}, Arcane Strike, and the other key feats by that point).

However, the "Dragons as Familiars" section of Draconomicon only gives minimum caster levels for chromatic and metallic dragons. The gem dragons come up in the "Dragons as Player Characters" section in the same chapter (only three pages later), so the book clearly acknowledges them; however, they are not (by RAW) allowed as familiars. The "Dragons as PCs" lists which of the core dragons match which gem dragons in terms of level adjustment and effective character level; do you think it would be a reasonable houserule to give each gem dragon familiar a minimum CL requirement equal to that of the comparable core dragon?

Tossing the numerical stuff I've mentioned into some tables, with specific info I summarized:


Gem Dragon
Equivalent Monster Manual Dragon


Sapphire
Copper


Crystal
Green


Amethyst
Blue


Emerald
Bronze


Topaz
Silver




Dragon Kind
Minimum CL
Gem Dragon available at same CL


Copper
10
Sapphire


Green
9
Crystal


Blue
10
Amethyst


Bronze
11
Emerald


Silver
12
Topaz



What do you all think of this? It seems perfectly fair to me, but it's always good to get a second opinion.

As a side note, are there any other feats that might be useful to make a dragon familiar more effective beyond the various feats that apply to any old familiar?

[Vaz]

Entangling Breath is always a good one for a breath weapon user. I personally think that that looks okay as a Familiar.

[Bronk]

I'd say it depends on whether or not the gem dragon's planar travel ability can be used on others...

Aside from that, the crystal dragon's breath weapon isn't explicitly resisted by anything in the game, and may even pass through 'transparent' walls of force...

[Extra Anchovies]

I think the plane travel ability would only apply to the dragon itself, since it doesn't actually replicate a spell and the ability only refers to the dragon traveling, without mention of possessions or companions.

You're right about the crystal dragon's breath weapon. The Topaz has an even nastier breath weapon, though: it's a cone of untyped damage, dealt in d8s. It's described as "a cone of dehydration that looks like a watery blast", but since no damage type is specified, nothing is immune to that damage either (at least not by RAW). And the die type is one higher than the crystal's.

On that note, which gem dragon would be the most useful to have as a familiar? Sapphire is pretty much out, being Tiny size; having one of the high-Int dragons would be an excellent combo with Knowledge Devotion, as they could put max ranks into Spot, Listen, and six Knowledge skills. Topaz is somewhat tougher than Emerald (one more HD, and +1 natural armor); its breath weapon is also one die type stronger and is typeless damage. The extra hit die also means its skills would all be one point higher than an Emerald wyrmling, but the Emerald dragon's at-will Object Reading seems really useful. What do you all think? If I took Dragon Familiar at 12th as planned, I could take either one right away, but I'm not sure which would be more convenient to have.