There's a few flaws with that though.
First, by the time you get a job, you probably won't be on PC any more. Your WPM will have changed by then. PC might not even be up, so they can't have concrete proof that you claim is correct.
Second, there are better ways of proving you have a good WPM than some wishy-washy claim about your posts on a forum. A WPM test isn't hard to do. All you need is a computer, a basic word processor like Wordpad or Notepad, and a special page with WPM on it. I'm sure they would rather have the concrete results from that than a basic claim about "I had x posts on a forum during this time". The WPM test is very structured and real to what you will do in the workplace, while on PC, your posts vary in length, and so will your WPM. Also, the posts on PC aren't going to be what you're doing in work, I can guarantee that.
As for the 10k, I don't think it's very impressive. This is a big enough forum where you can get it easy, I think. There's tons of threads in the fanclub section you can get easy postcount in, not to mention the DCC if it's active enough. There's also tons of sections where you can find threads to post in at least once, if not more. Anyone could get 10k with time and patience, really. Besides, it is just a number, after all, and it doesn't reflect quality. Would you rather see a member with 10k of one-lined posts that are almost spam or someone with 100 good, well-thought out posts?
Well, that's just my opinion, anyway.