In reply to MischaHY:
Sorry for the delayed reply - I was away, as Rob said.
I'm afraid I've never used or even seen the Western Summerlite so all I can say is that from a very brief look at their website it seems ostensibly quite similar to the Mythic 200: It's marginally heavier, it has slightly more down fill (though I can't see on their website what quality/fill power of down they've used), and it looks to have a similar temperature rating (though I'm not clear what testing standard this conforms to). Not much help I'm afraid...