Did he get to see that other gifted school? I wonder if he actually was in that environment you may have a better idea of which is better for him. Also, those kids might be at that level, what did they say about your son's level and accomodating that?
I know what it feels like to walk in a room of same age peers for your child and to see the level they are working and walk out with a pit in your stomach. I am settling in to the sad reality that there is no perfect placement for every child. I have been obsessing over K placement for our DS.