I had my son tested a few months ago also using the WPPSI with similar scores, from the piece meal information I have gathered the WPPSI only scores up to 160 and does not have extended norms. I have been reading through Hoagies and the Gifted Development Center website for info
http://www.gifteddevelopment.com/, there they describe the different tests, some of them have extended norms, but it seems like they use the Stanford Binet LM, the old test, to be able to make the high level differentiations. From what I have read the tests are all slightly different and you can not really translate one test score to another test.
Good luck I know I've felt overwhelmed with this info and what to do with my son regarding schooling.