I just want to throw my 2 cents in...
I had DS tested at 4.8y on the WPPSI and recently on the SBV at 7.8y (this second testing was for DYS purposes only since the original WPPSI scores were greater than 2 years old). DS did well on both scoring within a few points of each other on FS IQ. DS also excelled/ceilinged at NV on the SBV and Performance on the WPPSI. DS is a very VS kid - building Legos, blocks, stuff out of things, 3-D visualization, etc. Here's a quick link that describes VS learners: VS def
Additionally, the psychologists in our area have described the 2 tests as differing in that the WPPSI measures knowledge gained thus far, rather than potential wherease the SBV measures some knowledge but is able to assess potential better.
FWIW, I have had friends' children who have taken both tests and received highly dissimilar FSIQ scores (all GT but ranging from low end to mod or from HG to PG).
And lastly, we had DD assessed on the SBV only and DD's score was within 2-3 points of DS. I only mention this since DD did not present as GT+. I thought DD was bright and maybe MG but DD's scores were DYS worthy like DS's.

IMHO I would go with the SBV. Reason being DD not presenting as GT and being GT! Also, DS's scores were slightly higher on the SBV v. the WPPSI-III.

HTH, Good luck and please do keep us posted.

Feel free to PM me if you have detailed questions.

Last edited by momx2; 01/08/09 09:09 AM. Reason: typos galore!