Hi and welcome!
IMO, I would go with option one or two. The gifted school, besides being a much longer commute (which would therefore impact your daily lifestyle), sounds like they aren't looking at your son individually, but are instead saying that they are used to working with gifted kids and know what's best, which may or may not be what's best for your son.
A lot of people here have said good things about language-immersion schools, which option 2 seems to be for your DS since it's in English and not his native language. It's a way to challenge him without moving him too far ahead academically, which can be appealing.
I like that option 1 is the least expensive and that they, like option 2, seem to be open-minded about his placement. You hate to shell out too much money for early education if you don't have to.
Finally, there is something to be said about keeping him home another year. It doesn't fix the mismatch between your son and the schools, but it does delay the mismatch and saves you money. How good is the current situation with the nanny? Does your son get other opportunities to interact in a group setting with other children (of his age or of his intellectual peers)?
