The tester can make a huge difference to how fast the test is administered. But also at barely old enough to sit that test your child does not have nearly as much cruft to wade through before they get to their level. The SB5 has routing questions that provide a guide as to how far through the material you can start testing, which often makes the SB5 shorter, the Wechsler tests do not do this, so a 6yr old (who could sit the WPPSI still OR the WISC) is going to have a lot more wasted time on the WPPSI than the WISC. My 4.5yr was off with the pixies before she got to her level on the WPPSI, I cannot even imagine what she would have been like at 6. Where as the WISC would hopefully be pretty snappy (with a good tester) for a 6yr old, even a gifted one.
