Rails: How to generate and seed db with 100k random users with associations

I'm trying to seed my development db with an amount of records that more closely resembles my setup in production. The primary reason for this is driven by optimization. I'd like to test with real data but in different amounts, i.e with 25k, 75k, and 125k Users etc., all with associations. The only approach that I can think of is creating different variations of a dump, which would take very long because of how long it takes to delete records! How can one accomplish this task?