The update to 4.4.4 has made my S5 snappier, no more stuttering when swiping from screen to screen. Apps seem to load a bit faster though that could be my imagination. The update did not fix the music skipping issue for me. My S5 would skip when playing back music using Google Music, Poweramp, or any number of apps. The music would skip over Bluetooth and even when using wired headphones (Poweramp only).
That seems to have finally changed though. There was an update on the 14th that I downloaded this morning and one of the fixes specifically mention Bluetooth audio skipping. I didn't have any issues during my 15 minute commute this morning with Google Music (which I'm fine with using since it has Chromecast integration). Poweramp still skipped but I think that's the program itself. I was about to toss my S5 into the Ohio River and get an HTC One M8 but I think I'll keep it for a while now. No more Bluetooth audio stuttering/skipping.