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20deg is fine for western steel knives, by comparison you can go WAY down with harder japanese steel. But you have a trade off, softer steel tends to be high toughness with ease of sharpening... but...

Most of the time you can remove material from the back side of the knife (oposite side of where the serations are ground in) and just thin the edge from there. Or the ceramic crocks can help as well....

http://www.japaneseknifesharpeningstore.com/

Here is another link to get some stones and see whats out there. Some of it is just way over the top for a Wusthof though :w

With a Wusthof I wouldn't go much over a 1k, western knives tend to be softer and thicker than japanese knives, Not always but most of the time. So the sharpening and honeing of the knives is handled...