For the purpose of reaching uncrittability, defence rating and resilience do the same thing. Your percentage crit reduction from +def and resilience needs to add up to at least 5.6% to be uncrittable. It is true that resilience does not offer the avoidance that +def does though. There is no formal "formula" other than the fact I stated though (at least to my knowledge, although I'm sure you could find a relationship with some algebra). With your +def and resilience, you have plenty of room to drop some of either in favour of other stats.
Oh, one more little thing that my pedantic self couldn't help noticing. There is no defence cap. 490 defence makes you uncrittable, but continues to provide effect after 490 too in the form of avoidance + block. Sorry, little things like that get to me.
Also, since this is in the Armory Ratings & Suggestions forum, would you mind posting a link to your profile? I'm sure we can give some tips about what to change if you want to swap that extra +def for other stats.