I'm just reviewing Panasonic's new Lumix GH4 camera which can record Ultra HD video at 4K. The results are extremely impressive, but so is performance in Vegas Pro 13. I'm getting preview playback of a 3840 x 2160 25fps video clip at FULL>BEST preview quality at a rock solid 25fps. This is with GPU acceleration ON. I'm also able to render to eg SONY MP4 640x360 25P with no problems, no artifacts, no black frames etc. with GPU acceleration ON. Render took 7 minutes for a 3min 15sec clip. All this on my 'old' Core i7 3.7GHz with 16GB RAM.
Pretty darn happy with this!
Oh, and one more lovely thing - I was able to open the VP13 project in VP12 with no issues - haven't been able to do that before...
David S