RegDCP - 4:58 pm on Sep 15, 2012 (gmt 0)

RegDCP, 5%

I don't think that Google is going to penalize on the basis of overall percentages.

I DO think that they are going to apply their penalties based on the misuse of linking.

If we look at a 100% organic link profile, the use of anchor text is not under the control of the site being linked to, but is up to the (organic) linker.

Using a base percentage for a phrase is further complicated by the efficiency of the linked page's call to action.
A very clear CTA would increase the percentage of a specific keyword phrase being used as anchor text.

Your 5% off topic - non-relevant link profile is 24,443 links.
This is a significant total, and I would think it to be well above the trigger point of any spam link penalties.

If such a kw penalty was awarded (for over and above what could be interpreted as natural distribution) would it expire after a certain period (90 days?) or it is permanent?

I have been working with clients in the same position and found that the penalties will follow across to a brand new domain, if ownership is linked.

Since it has been 144 days since Penguin, I would surmise that it is not 90 days.

The only thing I can think of is to start a brand new domain under different ownership/IP block.
Since Google is also a registrar, I am not sure if privatizing the whois would work.