If OP was buying a house solely based on slightly raising their child's chances of a TPMS STEM slot, they would buy in-bounds for East Silver Spring ES, which feeds to TPMS.
Yes, it is a GS5 as opposed to PBES's GS6, but the test scores show that similar kids do well at both schools. The "advantage" of ESS for TPMS admissions is the size. About 75 kids in 5th grade as opposed to 150. Of course, Piney Branch has its own CES, which is a tremendous draw as well.
It would be silly, though, to buy inbounds for either PBES or ESS "just" for a bit of an edge in TPMS admissions. You would need to like the schools, the neighborhoods, and the high school feeder. It would need to work for your commute, and your lifestyle (small lots in both neighborhoods, with a lot of population density and multi-family dwellings).
For what it is worth, I'd recommend East Silver Spring and Takoma Park even without the TPMS advantage. Both are great neighborhoods, accessible to amenities, and full of interesting people - many of whom are doing a lot of good in the world.
It's not everyone's cup of kombucha, but it's a great place to raise a family even if your kids don't get into any magnets at all.