Stability? No lag? Not having to mess with wifi to make my phone NOT lag or take 5 seconds to wake up? It's just the flagship - no reason to expect it to perform well I guess.
I have no issues with my Icon, after DP download 8.1 , no lag, wifi works, phone wake up in less than a sec. I have stressed this phone out with open programs in the back ground, movies , games, etc. to find lag, and problem , but it just keeps on working like it should.
you might want to try Storage Cleaner to clear out the fragmented junk. , and I believe it relines the programs for faster search. also try opening and closing Kid Corner, I believe this approach allocates space for the Kids Corner, in doing so by compressing your programs on your side, and removing spacing, and unnecessary fragmented markers, which happens from installing and removing programs. I can't prove any of this other than my phone run's great.