Peppers will grow at any temperature that is comfortabke to you. Certain peppers will grow and produce fruit during the winter. One way to create stonger roots and lush vegetation without fruit production is to feed your plants with a fertilizer that is slightly higher in nitrogen than phosporus or at esqul amounts. If the termperature drops lower than what is comfortable to you they will go to sleep and stop production of leaves and fruits. That has been my experience but others in colder climates may have better or different advice.

if the plants are badly stunted, why not just start fresh next year with new seed and do it right from the beginning? I mean, unless you're going for a bonsai or something.

Yep, if it gets cooler they will likely quit blooming. However, they will likely not be growing a lot of root system either. You can manually snip the blooms if you like or just wait for them to set fruit and then snip them. That is what I would do if I was trying to overwinter a pepper plant. You are in zone 5 and you don't really need those plants to get too big too fast. You won't be able to get them outside for the summer for many more months.
I would keep them trimmed back for a few more months or like the other poster stated, you may want to just start over with new seed in a couple months.
Bruce