The membership page of Sunrise Valley states there were around 200 students in AAP at Sunrise Valley last year. So that would even out to be about 2 classes of 25 students for each grade.
http://schoolprofiles.fcps.edu/schlprfl/f?p=108:107:2086267516894024:::
0_CURRENT_SCHOOL_ID:325
Flint Hill shows approximately 105 students in AAP. I'm not sure why the number dropped down about 20 students in May to 86. Anyway, that would be about 25 students as well in each grade although I think for LLIV they do not have to keep these classes self contained so the class size could be higher.
http://schoolprofiles.fcps.edu/schlprfl/f?p=108:107:4181324604157643:::
0_CURRENT_SCHOOL_ID:063
Sorry, I know little about the two schools although they both sound like two good options. My guess would be that more Flint Hill students opt for Louise Archer than opt for Sunrise Valley since Louise Archer is so close by to Flint Hill. I also think a lot of Louise Archer students use Flint Hill for aftercare which is why their SACC list is pretty long. Not sure if SACC is in the mix of your decision or not. Sunrise Valley I see has a FLEX program which is basically a language program that you have to pay a couple hundred extra for. It looks like they offer it in the morning and afternoon.