My son is growing up bilingual, but his English is currently stronger than his 2nd language. We're looking at some similar schooling options and issues with distances, barely missing the cutoff, and tuition costs, although we only have options like your 1 and 2, no gifted schools here.
I am leaning towards an education in English for DS3 (either an expensive private w/commute or homeschool) simply because in our situation it provides more access to materials and other opportunities in the long run. Because I don't think school in general is going to be a good fit for my son in terms of personality (non-compliant, anxious, perfectionism, shuts down in public), learning style (very active/imaginative), and limited self-control, I am avoiding sit-down school for a while instead of pursuing early options. Our tentative plan is to homeschool K-2 or so, until hopefully some of those things improve with maturity, then for him to test into the grade at the English school that will be the best balance for him socially and academically.
I share this to explain why personally, if you could find the right type of nanny, I'd vote for that option and let him pursue his interests at home. If you're going to be somewhat locked into your school choice, then another year will give you a clearer picture of what kind of environment will have the most benefits for your son. But I know that every child is different and your son might be ready for more structure. I wouldn't not challenge him now for fear of future boredom because it's so hard to know where your DS will be at that point; better to find what works for him and keeps him happy now I think. Good luck and I hope you let us know what you decide.
