Version 4.2 is up, which includes 50 Steam achievements. Please let me know if anything is slower due to the plugin I am using. I don't think there should be any problems. By the way, if you are playing in editor mode, you can't unlock achievements.
I'm gonna release v4.2B tomorrow with a couple other improvements.
EDIT: Alright, version 4.2B is out. You can look at the updates text file for a full list of changes. Now I'm going to the bar to drink and grade tests.