Yes having accelerated learners can make finding a best fit school more difficult. I suggest you Consider all options available to you at the beginning of each academic year. Montessori should be able to cater to you for a few more years yet. Especially if you happen to be at a good one!
Finding accelerated public schools is often difficult and then determining if the level of acceleration will be enough is just as difficult. If you can find one though they are often fabulous.
Home schooling is a firm option to consider but it isn't the only solution. Homeschooling does allow you to continue to advance from where your child is at without any wasted time. Many EL children end up being homeschooled because there is no good fit in a public or private school for them nearby.
Your child's education needs will differ throughout their schooling. It's important to remember that and reassess when it isn't fitting any more.
Also you need to remember to be an active participant in your child's education at all levels. This alone will make all the difference. Smart kids need parents to advocate for them as much as struggling kids do