Christina B.,
First of all, welcome! Those are excellent scores - you obviously have a smart little guy on your hands.
Unfortunately, I am not an expert on testing, so I will let others answer your more detailed questions.
In general terms, I think your ds most certainly did hit some ceilings. Hindsight being 20-20, it probably would have provided you with more information had you waited until he turned 6 and tested on WISC IV.
Others can correct me if I'm wrong, but I believe you could still go ahead and test on the SBV without waiting, if you were simply trying for a DYS qualifying score.
Has he done any achievement testing? That's the other part of the DYS equation. If his achievement testing was strong, there's always the chance he would be accepted with a "not-quite-there" WPPSI score. I know it has happened in the past.
I hope others will chime in to answer your questions in a more detailed way. I just didn't want you to think your question was going unread.
