Having bought a new camera, I have been working hard in rendering to the optimal image quality with Vegas. One of the issues I had was stuttering playback in the final product, especially with pans and fast moving objects.

Of course, I did the essential thing, matching project settings to the video file. That was ok. But today I was watching at the rendered file properties of the mp4 in Windows explorer and I noticed that it said 14fps. I double checked via Vegas itself, and yes, Vegas also says 14fps.
So then I checked my customized template; sure enough, I had selected 29.970fps.
Details:
Mainconcept avc/aac
hd 1080p (1080x1920)
profile: main
field order: non (progressive)
pixel ratio: 1.0000
Bitrate max 16000/average 10000
Cuda enabled
This setting would produce a 14fps video

So then I unchecked 'allow source to adjust framerate'.
The result now is a file at 29.970fps with FLUENT pans!

The camera I use is a Nikon V1. I cut and color grade these movs in Lightroom 4.4 (64bit) and export them (transcode), and it is these exported files I put on the Vegas (vs 12/64bit) timeline;

Hope this may help the community.