Welcome!

I had my 5yo tested with the WPPSI last fall. I'd be careful with that test due to ceiling issues; my ds hit 5 ceilings, so the test didn't tell us nearly as much as it could have.

When does he turn six? If it's not too long, you may want to wait and use the WISC, which has a higher ceiling. Otherwise, I'd probably go with the Stanford-Binet 5.

Good luck!

Mia