My DS7 took the WPPSI at 5 and the WISC at 6 and 8 months. The WISC provides more information and having GAI as well as extended norms helps at ceiling levels for a better picture.
From what I have read the SBV is a more abstract reasoning test and if the child's strength is verbal they might not do as well as on the WISC. If the child's strength is abstract reasoning then the SBV may better suit their strength.
For DS7 the WISC showed his strengths verbal and perceptual (abstract) and also showed his weakness (working memory and processing speed).
