I know what I did, but I'm still not sure it's right.

 

which should I take, the stinger (doing so would keep my (20) safe from skill attack) or the (12,12) (to get it out of the way and keep from rerolling even higher than my (20))?

mildly counterintuitive, but actually an easy computation.

 

It's not hard to do the explicit math here, but what's your intuition? I must attack with my (12), but should I take the p(10) or the (X=4)?