Usually you want to consider your M variable a lot sooner than this it can be a lifesaver in helping you make decisions at the table under pressure of a dwindling stack.
M = Your stack size / total in the pot before each hand
you how many orbits you will last if you don't play a hand.
Use your own example: M = 13k (your stack) / 12k (6000 Bb + 3000 sB + 3000 antes) = 1.08
To put things into perspective you should be open shoving complete garbage almost any two cards with an M less than 3, so K8s is like... beautiful.
Aim to always keep an M larger than 8. Anything between 5-8 is pretty dire straights and you need to find places to make some moves before its too late again.
M greater than 15 and you are on the right track. Greater than 40 and you are kicking ass.