Stay away from down, except for winter or above tree line camping.... rains happens unless it's below freezing....
I used to work an outdoor outfitter.... after leaving the Corps...
Higher end bags are lighter and more accurate about temp ratings than no name bags...
I have two North Face bags... one is 17 years old, the other is 10!years old- it replaced (under warranty) one that I bought 25 years ago...
A hint about making a bag cover more temp ranges... firstly, bags are rated with used in conjunction with an insulated pad!!! In a tent!!!
A sleep bag liner cuts 5-10 degrees... as does a sleeping bag cover ....
a military poncho liner adds about 10 degrees to a bag...
So I use a cats meow bag, use a silk sleeping bag liner, Cary a poncho and poncho liner... I can use the liner and leave the bag open... if it get cold, insert the poncho liner... still colder, zipnit up some... still too cold? Wrap the poncho over the bag and tuck it under the bag.... so a 20 degree bag can go to about zero for this native Floridian!!!