UKH

I am looking at a traditional elephant's foot half bag, to be used in conjunction with a puffy belay jacket for alpine bivis, including some winter conditions.  

Down filled pants would also keep my lower half warm and have the advantage of greater mobility when wearing them.  

What says the collective?   Half bag or pants?  

Full bag

Assuming bivis on routes.

Summer light synthetic half bag , I made my own.

Winter full bag , and beware of spindrift.

Edit. I assume you are asking for European alps