If you do test early, just go into it with the understanding that it may be recommended that re-testing be done between 8-10, due to the potential instability of earlier scores (lower or higher). Even when I had DD tested at 7, they recommended testing again later. But we're just going to see how the school testing turns out (achievement and CogAT) before seeing if we need to followup in order to access services.
I, personally, placed a high value on 'decent' school zone when we needed to move, when my DC were under school age, only knowing they were suspected GT. We didn't end up in the rumored 'best' districts, because of commute and cost, and that was okay. We weighed a lot of factors, not just schools (commute time, housing prices, taxes, flexibility for future employment changes, kids in the neighborhood, schools, etc). The real issue will come down to who is at the school when your child is there, and that can shift yearly, just as the child's needs can shift. Our district is a growing one, adding schools and shifting teachers around. Programs can be cut, you just can't count on that. What you can count on is your own involvement and knowledge, and that your awareness and feeding your child's interests, reading, all of that will contribute to a love of learning.
If the zone that has the gifted school is within your grasp, and fits your other desires and limitations, so that if the child doesn't 'fit' within a gifted school format, are the rest of the schools in that district decent enough to make the choice easier? If it's one program in one school in an otherwise less desirable area (too far from work, family, etc), it makes it tougher!
Being where you are now (like here, earlier than I was), you will be able to go in knowing what to advocate for, understanding your child's needs, and that will make a big difference.
