Totally agree with the real estate agent, although I thought realtors couldn't talk about the quality of schools when trying to make a sale. ??
In any event, I live on the Wootton/Quince Orchard high school zoning line, or whatever it's called. Right now we are zoned for Wootton, but I think Quince Orchard is a lovely school. I have friends who have had their kids in both Northwest and Gaithersburg, and they have all been happy. Gaithersburg has had some historic problems, but it's getting a new facility, which might boost morale (and therefore performance) a bit.
And keep in mind that there is a STEM magnet program at Poolesville High for the upcounty region. It's similar to the STEM program at Blair, which is the one most people are familiar with. And the Richard Montgomery IB magnet program is open to all county students if they apply and are accepted. In other words, that one isn't regional.
If you don't know about School at a Glance yet, here's the link. It provides some comparative date for each school.
http://www.montgomeryschoolsmd.org/departments/regulatoryaccountability/glance/