There is a reason that the homes are priced higher in the towns you have been considering. While a nice small town, Portland is not in the same class as those other towns you are considering. The other towns mentioned are upscale suburbs. Portland is a small town across the river from Middletown. It has some very nice neighborhoods and a couple of great golf courses.
Schools in Portland perform above the state averages on the Connecticut Mastery and Connecticut Academic Performance tests. Class sizes are reasonable (around 20 students per class). You can read additional information on the schools in Portland on the Connecticut State Department of Education website below:
Strategic School Profiles by District
I should note though that Portland does not have great access to highways. To get to it you must cross the Aragoni Bridge to Route 9 in Middletown which can be difficult during peak traffic periods. Portland only offers limited shopping in town so you may have to travel to do shopping. Also note, that while the schools in Portland perform well, they do not perform as well as the other towns you mention which are among the best in the state.
If you would like alternatives to the towns you mentioned, consider Marlborough, Hebron, Granby and Burlington. Jay