I've had the opposite experience with Elixers. They sound great right out off the bat, and stay great for a few weeks or maybe even as much as 2 months (depending on use and humidity and cleanliness, etc), but when they start to die they die an ugly nasty death. Specifically they lose the ability to stay in tune - they seem to get "stretchy." Just my .02.
This observation was probably 3-5 years ago, but I never went back because I felt I could get better life out of metal strings, with an occasional swipe of fastfret to maintain brightness.