The nexus 5 is still an amazing phone, no lag, screen is great and size is just right for your hands.
I haven't even looked at the n6 as my N5 is so good! Had it from launch day and its still faster than most.
My only complaint is the battery, fix that and I don't see why most people would need much more from a phone.
Makes me wonder if the improved battery enhancements in Lollipop is simply the battery saver option, which you can set to enable at a certain battery %, which basically just disables everything, or whether there are improvements throughout the OS.
I've noticed gains, a lot of my usage is off screen e.g. streaming spotify, podcasts, syncing of 3 emails, whatsapp/hangouts etc etc.
4.4.4: usage 5-7hours 2-3hours screen time
5.0: usage 8-10hours 3-4hours screen time.
I'm going to say I get a solid 20%-30% increase, your milage may vary.
That's impressive
Expect awesome reviews, Android L has an amazing level of polish, UI is a delight and I think its better then every, and by quiet a margin.
Hope so. It's a bummer that Xposed won't work with L and ART.