The original script I used to find the answer used some old values with runes. I re-ran my methods again and did a better job honing in on the actual break even point. The new script is attached:

without I.E. (2x crit dmg)

- base < 36.5% => stack more crit chance runes
- base > 36.5% => stack more crit damage runes

with I.E. (2.5x crit dmg)

- base < 56.5% => stack more crit chance runes
- base > 56.5% => stack more crit damage runes

Meaning if your base crit chance from everything

*excluding* runes is greater than the above thresholds, then stacking more crit chance runes will

*lower* your dps. Having more crit damage from items beyond 2.5x will only serve to raise the point at which you reach this threshold of stacking crit chance.

These thresholds are fairly broad, meaning just slightly above or below the threshold, your dps does not differ significantly from the optimal dps.

At the break even point, it is interesting to note that in order to obtain optimal dps, you would need to make a funky combination of crit chance and crit damage runes, rather than stacking all of one or all of the other.

__At the break even point, if you stack all crit chance or all crit damage, you will have minimal dps (but it's not too far off from maximal dps).__

EDIT: It would appear that I got pretty much the same result as Umbrage in the posts above mine. I think it's safe to say that if two people confirm it independently of each other with different methods, then we have our answer. I encourage the OP to edit his original post to reflect these conclusions so that other people can read them. Currently your post does not contain a correct break even point and your conclusions are wrong and misleading.