How is the celestial template applied to a paladin's mount?

Question

At 11th level, a paladin's mount (if he took one) gains the celestial template. Most of it is straight forward; it gains darkvision 60ft., it would have 9 HD at the time, so it would gain resistance 10 to cold, acid, and electricity, and DR 5/evil, and gains smite 1/day. That's all straightforward enough (though if I've misconstrued anything, please don't hesitate to speak up.)

Then we get to the part about Spell Resistance. The template says that the creature gains SR='New CR'+5. Well, what would the CR of an 11th level paladin's mount be? And would adding the template increase it?

I would think that an appropriate SR would just be the paladin's level +5, as four levels later it becomes paladin's level +11, but I can't find anywhere that it makes the destinction.

If there isn't a rule for this, fine, I can accept that. I'm mainly asking; Does anyone know of a ruling about this, and if so where I could find it?

Beyond that, if anyone has any suggestions, or notices something I missed or messed up regarding this topic, I'd be obliged if you'd let me know. That said, I am primarily looking for a ruling.

Answer 1

As a class feature, a paladin's mount does not have a challenge rating, since it's already factored into the Paladin's challenge rating The same applies to animal companions and familiars. While it is never explicitly stated, defaulting to the person whose class feature they are does make sense in circumstances like these.

As such, Paladin's CR +5 seems like the logical conclusion but this is a situation that doesn't seem to be covered by the rules, despite that it should probably have been. By a very strict reading of the rules, they would probably gain a spell resistance of 5, which at level 11 is useless.

Either way, it's obviated just a few levels later (as you pointed out) and barring an official ruling or erratum somewhere, Paladin's CR +5 seems the closest to the rules option we have available.