For a child closer to 6, I'd definitely encourage waiting, but at 4? It might be worth the faster results.
4yr10mo,
Sure if the school will pay for the WPPSI at age 5, why not? But if one has to pay out of pocket, why not get the SBV, particularly if DYS is a possibility.
I'm not sure if there is a GAI for WPPSI.
I found this:
WPPSI-III (Wechsler Preschool and Primary Scale of Intelligence-Third Edition) The WPPSI-III offers improvements over its predecessor for gifted children. It appears to be a better diagnostic test and it emphasizes abstract reasoning well. It has two forms: one for children ages 2-6 (2 years 6 months) to 3-11, and one for ages 4-0 to 7-3 (we prefer a WISC-IV at 6-0). The form for very young children is short (4 required subtests) and only Object Assembly is timed (rather generously). The portion for ages 4-0 and up requires 7 subtests and has a good mix of verbal and visual reasoning in a child-friendly test (administration is more comfortable than with the WPPSI-R for little ones). The test does have a Processing Speed Quotient, but only one of the two subtests from which it is calculated is included in the Full Scale IQ score. This is a timed handwriting-like test. Slower processing speed on handwritten paper-and-pencil tests is common in the gifted and should not rule out admission to gifted programs.