...have you guys been getting away with?  In the past, I found you'd have to finally bounce to clips with V-vocal or things started getting grumpy. 
I haven't really reached a limit yet with Melodyne and have even thrown entire vocal tracks into it...both as a whole and lots of separate clips.
Since my computer and X3 upgrades, I haven't used V-vocal, nor did I use Melodyne on my old computer.  But it seems there's no match as far as stability.
 
And lastly...do you feel the need to bounce to clips before mixing?

It's not the case that everyone found the need to bounce V-Vocal clips
The need always seemed to be system specific
 
Speaking from my own experience, I ran a project several years ago which consisted of 75 tracks, multiple vocal clips, all with live unbounced VV clips and all of my soft synths were running without freezing
 
What's even more impressive was this was on a machine running XP32 bit with 4Gb of RAM and a Q6700 cpu
 
As far as Melodyne is concerned, I can't really help as I still use V-Vocal.
VV's only drawback for me is that opening old projects in X3e invariably leads to crashes when trying to edit existing V-Vocal material, but it's fine on new projects
 

This is what I do.
1) Split clips of track (verse/chorus etc) if necessary.
2) Clone track
3) Create region FX on clips on cloned track using Melodyne on cloned track.
4) Do the business.
5) Bounce the results to a new track
6) Archive off the first two tracks.
 
With this sort of technology I'm ultra cautious.
 
Ta.