I had an Antelope, now use a Versalite. Same size and same basic temp rating, just a lighter bag. I certainly use mine here in Montana into November, as long as we don't have an early winter with sub zero temps, in which case either the Antelope or Versalite will need an overbag and perhaps a VBL.

I buy all my WM bags from Hermit's Hut because they offer free overfill (which I've had on all 8 WM we've had at our house).

https://www.hermitshut.com/product/western-mountaineering-antelope-micro-fiber-sleeping-bag/

“Perfection is Achieved Not When There Is Nothing More to Add, But When There Is Nothing Left to Take Away” Antoine de Saint-Exupery