This may not be related to Meteor but when WiredTiger engine is used with compression, does this affect Meteor in any way?
Your app should be fine that is if it has that much data to begin with. You can dynamically configure the wired tiger block cache to suit your needs if required. If you are very paranoid about compression taking a hit on your system, Install zlib1g-dev, libbz2-dev, libsnappy-dev and test compressing and decompressing a an 8kb document to give you a good idea. You could also ask this on stack overflow as it will fit the crowd there much better than here.
Just to add - there was a discussion about this a while back: