What order of magnitude should I expect the parasitic capacitance to be for a solderless breadboard?
2-3pF row to row, and 20pf rail to rail, but checkout this video...

https://www.youtube.com/watch?v=6GIscUsnlM0&amp;feature=youtu.be

Probably a bigger issue with BBS is often the flying leads and longer legs on resistors etc. The extra inductance will also give you issues at higher frequencies. That and fairly high point contact resistance.