I only have advice on the SB-5 since my DS6 took that at 4 years 9 months old. Funny enough--we had some ceiling issues as well on this test but at the time we needed something to convince me that he was GT and needed to go to new school. I'm pretty sure we would have had ceiling issues on the WPPSI despite the fact that he was still less than 5 years old. My son is also considered more verbal and mathy and that was what his test results showed.
I don't regret using the SB-5 and actually our tester told us that she preferred the SB-5 over the WPPSI despite the usually lower scores. She actually warned us that his scores on the SB-5 might be lower than expected but would still give us a good idea of his IQ.
If we need testing again in the future for DS6 I think we would choose the WISC.
ETA: We posted at the same time and I just want to add that you should not feel bad about testing for DYS. The only reason we did achievement testing on DS6 at the age of 5 years 1 month was to get qualifying scores. I doubt I EVER would have subjected him to that type of test if we didn't need that score to apply. I don't think it told me much except that he was academically ahead, could read, and could do basic math. I knew that without the test.
