The jerky frames you mentioned is the result of fluctuating fps from a lower number to something much higher.  Panning or moving quickly should not cause any hiccups @ 60fps assuming it doesn't drop too much below 60.

Stutters will occur when your frame rate is constantly jumping from 50 to 100, then down to 50 again and up again to 120.  When you lock your fps @ 60 for example, you may get a minimum of 25 or 30 at payware airports with 100% traffic.  So going from 30 back to your target 60 is only 30fps difference.  If you get a minimum of 30 when set to unlimited and it jumps to 100, that is a 70fps difference which will give you more noticable stutters.

 

Even though your monitor's refresh rate is 60, the video card is still pumping out all the extra frames above 60.  It will work harder than when you have it locked.

 

But if you're getting better smoothness with unlimited frames, then use what works best for you.  

 

I'm running on a plasma with 500hz and I get a lot of stutters when set to unlimited. 

 

As for Vsync, I leave mine off because I don't get any image tearing in FS9 no matter what fps I'm getting.

Thank you for the info