nah, i managed to undervolt the nexus 4 by 100mv and it worked fine, think I settled on -125mv in the end on the nexus 4 because -150mv caused reboots and crashes, there's posts in the nexus 4 thread anyway about it all.
-50mv is imo perfectly do-able for every nexus 5 absolutely no issues.
if you are going to push further, i suggest that you do not set the voltages to be set at boot, yet require manually setting each time you start the device up.
that way if it does start to reboot or crash after it boots back up it will be back to stock voltages, rather than constantly bricked until you flash stock rom or something or flash another kernel.
i will try -75mv next week.
-100mv the week after.
repeat until i get crashes and reboots. when that happens go back up two notches (not one because you can never really stress test a phone for any situation) to be on the safe side.
i reckon this should do -100mv fine but i have enough time to test it for a week at a time until i'm happy.
on another note snapchat is buggy as hell, the developers need to re-write it from scratch i reckon.