You are right about the difference between Drats and GWPs. Drats are registered to a German standard, and only dogs that pass their (VDD-the german standard) field tests are allowed to breed as Drats. If they don't pass in two trys, their papers are stamped "unbreedable". (I may be corrected by someone who knows more, but this is what I got out of my research). As a general rule, the Drats requirements are more strict than the GWP, which is registered through AKC.
Another site to look into is http://www.drahthaar.com/
, this is the official Drat page, there is a link to an article on there that explains the Drat vs GWP debate. The site is really tilted towards Drats, but nevertheless explains it.
I have friends who have and breed Drats, they are a awesome dog. Hunter and great companions, but in my humble, average income opinion, a GWP will fit my bill for half the money. I am not looking to start breeding, doing field trials with only Drats, or lifting my nose to other dog owners (Drat owners sometimes think they are better than others [img]/ubbthreads/images/graemlins/smirk.gif[/img]).
As far as behavior, I think they are similar to GSPs, a little hyper, destructive (chewing) when they are young, but I know for a fact they do grow out of that. Health wise, I think they are pretty solid, most breeders check their dogs for hips, vision, etc. I read they do shed "lightly" year round, but not real heavy. Less than a lab I would think. Also, several references have said that GWPs are more of a people dog than GSPs, and they are happy in the house, with people. (I don't really think any dog would rather be outside, but that is what they said)