First ... welcome to the board; I'm really glad you found this community and should find a lot of support here.
I think you know the answer to help with all your 'unanswered' questions ... you are the prime example of when to test. Look for someone who specializes in gifted children not just a basic tester. To answer your question of why test? You and your son are at a brick wall and the more data you collect about his LOG and especially the sub-scores from the test; the more you will have an idea of where to go from here. You haven't failed your son because you are open to the idea and researching it. You understand that what is in place right now isn't working and this is the main reason you need to test.
And if my instincts are accurate; I suspect you are dealing with the top of the scale on the LOG (level of gifted) and more than likely your son is level 5 on Ruf's levels. (Deborah Ruf's book 'Losing our Minds' is a great resource if you haven't read it yet.) What does this mean? It means that his age peers just won't get him and he doesn't get them. It also means that he isn't being challenged at school and though he has amazing motivation at home, he could potentially be suffering and get to the point that he hates school and learning. HG+ kids are high risk kids.
Testing him would open the door to places like DYS and kids he could relate to. You mentioned your husband wanted to place him in a special school for the gifted... is this not a possibility now? I know you talk about your son not wanting to move out of his school for fear of making new friends but maybe if he spent some time with the school observing ... he just might find a friend or two there and that alone might ease his concerns.
I'm sure others on this board will offer more advice or should I say ... more valid advice since their own children are closer to your sons age and/or have experienced what you are going through. My DD is only 3.5, but I completely feel for your son and hope you can find a solution that works for your family. He sounds wonderful and I will look forward to reading more about that amazing boy you have.
