I've used U99's as 'front of kit' mics & about a foot & change away from bowel loosening SVT rigs with nary an issue... I'd say it could take a loud singer without breaking a sweat!
For the record I'm doing now we've been alternating between a Dragonfly Deluxe and a Sony C37a for the vocals... both into a UA6176. The mics couldn't be more different but they both sound great... depends on the song. For the more crankin' tunes where the vocals are belted the Sony is great, takes it in stride without getting harsh on top.
J. 'Moose' Kahrs
producer|mixer|recordist MooseAudio.com mooseaudio.bandcamp.com
All you need to make a record is a mic, some tape and maybe some bad reverb...