Even if you don't get testing done, perhaps you can advocate for a skip. Sounds like he should go into 1st (at least)--I'm one of the advocates for skipping K.

I've heard the schools in Philly are usually not very flexible. There are some good charter schools around, and sometimes they have long waiting lists. You might want to research those as well, because it's easier to get in at the beginning rather than older grades--usually. Charter schools may have a more enriched curriculum and be more willing to work with you (or maybe not).

I went to JR Masterman (public gifted magnet school) in Center City, but they don't start till about 5th grade. I had to take a train & bus every day starting in 4t grade (Masterman used to start that early), but it was worth it--a great school, and I understand it's still the best.