My son did the WPPSI at 5.3 (the private gifted school accepted only this test) and he hit 2 ceilings in the Performance section and 2 in the verbal which makes the test kind of useless for truly understanding his strengths and weakness. I don't even think of him as a PG/genius kind of kid. I would absolutely recommend waiting for WISC.
Also, for many gifted kids processing speed lags the other IQ measures. WPSII doesn't have a way of calculating a general ability index without processing speed, WISC does.
