After spending the better part of the day trying to find out why the fsck my console script for importing a dataset through SQLAlchemy needed just above 7GBs of memory before barfing out and swapping like a madman, I finally found the solution.
Make sure that Pyramid’s debug toolbar is disabled. It’ll keep an reference around to all queries ran through SQLAlchemy (for... well, debugging purposes, obviously). This causes an issue if you’re running a very large number of queries, and you’re not going to use the debug toolbar from the console anyway, so... get rid of it.
I created a second version of my development.ini, a development_console.ini that doesn’t load the debug toolbar, and finally stuff Just Worked™ again.