If you can have more tasks for your monthly tasks, they absolutely need to be harder. In their current state, I don't think they need more than a small bump in requirements (like 33-50% increase tops) - so not 27 to 50, but rather 27 to maybe 40. Or 180 kills with primary to 250.
I think there needs to be a balance where it's not a grindy pain in the ass, while also not being something you get done in 5 hours.