I think trying to nail exact percentages is just going to give you a headache.
My general rule of thumb is to use 1/3 naked 1/3 generic and 1/3 optimized give or take (this will include the exact anchor, partial, LSI variations, and niche related).
This will be applied to mass link building ie. bookmarks, wikis, pdfs, profiles, etc.
Then with high PR quality links you go straight for the jugular of just optimized anchors (but again a mix of exact, partial, LSI, and niche related). Your site is already anchor diverse from the 1/3 1/3 1/3 backlink profile, now you can concentrate the better links for your money keywords. I firmly believe that using exact anchor in all your links is not only dangerous, but will become less and less effective. Google will decide what your page is about from your onPage factors, a few exact anchors are great, but partial and LSI will work just as well and safer.
Most penguined sites are the result of over optimized anchors IMO. It's one of the easiest metrics for google to detect. "Aha, this fucker has 50% links anchored with (learn spanish today), his site title is (learn spanish today) and his url is (learnspanishtoday.com), he's attempting to manipulate rankings and taking away our Adwords revenue for that keyword >>>> Penalty!