I'm on X3 Producer.  I have a high end PC with an i7-3770 cpu, SSD and 32 GB ram.  But I am using the onboard Haswell graphics support.
 
When I bring up many of my VSTs while playback is going, then tweak the UI the audio stutters badly.  Specifically the Blue Tube delays and TH2 (which I've upgraded to TH3) suck when tweaking in realtime.
 
I'm wondering if adding a separate graphics card would solve this.  Do others see this same behavior with their systems?
 
Thanks!
 

Hi. Which kind of audio interface do you have? I do not think that the graphics card would cause clicks / stuttering. Have you tried to increase the audio buffer? (I had an onboard graphics card in one of my older pc's, and it worked fine)
Best of luck.

I agree with Zargg on this. try playing with your audio buffer.
I will say though, when I added a video card on to my work station, it enhanced my experience and seem to free up some lag.
but I cant say weather or not it would solve the audio shudder issue you are having.
you didn't mention what/if any audio card you are using ?