Worked at a school where we used sleeping bags by the hundreds. They were used 3 weeks at a time then laundered. All synthetic 20 Degree bags.

They all performed the same warmth wise. And they all were toast after a couple of seasons and then good only for warm weather.

One sure killer of synthetic bags - drying with high heat. You can measure the shrinkage in length and loft after one hot dryer run. Best to air dry, maybe tumble low heat or without heat a few minutes before storage.