I'm not a video care expert but I can tell you what my experience has been, for what it's worth.
I have edited numerous HD videos with my previous 5 year old desktop w/NVIDIA card using PD8 ULTRA with no hanging problems. I purchased a new computer w/Intel Core i7, 9 GB RAM, and ATI Radeon 5970 g-card. I installed PD9 Ultra at that time and have since had issues with PD9 hanging at various transitions while producing HD video. I have maintained toe latest ATI drivers installed. Unfortunately, I gave my old computer away so cannot do any test comparisons between ATI and NVIDIA. With PD9 build 2702, I could uncheck the Preferences>hardware coding box and stop the problem but resulting video was poor quality. I have now installed patch build 2930. I must still keep the hardware codeing box unchecked but video quality is very good.
I have noticed numerous posts at this site describing the same problems; from what I see the problems are more prevalent with ATI cards; those with upper end NVIDIA's do not appear to have the same issues.
Note: I have never had problems when editing stadard video whether the hardward coding box was checked or not; only issues with dealing with HD (mt2s). Hope this helps.
Eugene88240