Hi TXMom.
I second Dottie's "Wow". My son took the WISC-IV as part of an acceleration assessment six months ago (at the age of 7 yr. 5 months). They may have given him other tests as well, so I can't say for sure, but I think they broke just the WISC-IV up into separate days? (He was pulled out multiple times over a two week period for all of the testing.) If not (and they did do it all in one day) he at least had a long lunch hour and recess to run around and burn off some of the test fatigue. I can't imagine him doing both tests back to back. That is completely insane.
I would add that many people have said that you need to find a tester who is experienced in giving the test to gifted kids. Gifted kids tend to answer more questions correctly, and hence have a much longer testing experience than most kids. Something that I recently learned is that the WISC-IV has an extended number of questions at the end, which can lead to a higher score. Someone else should really chime in here, but I don't know if many non-gifted testers know to keep asking questions if the child has hit the apparent ceiling on the test. (maybe the questions have always been there, and they are appending the scoring only on the Technical Report #7 for the WISC-IV?) But is seems like I have read of parents who were not sure if the tester stopped early with their child or not.
I'm new to all of this testing too. Hope this helped you some.