Hi there. I have an i7-2600k and as GPU HD6870 , Win8.1Pro , Vegas 12Pro . Perhaps i can help you. On my PC Quicksync operates in Vegas with SonyAVC , but not with any framerates. I found out when vegas rendering Videos in 1080p30, quickync does work with both settings, QS-Quality and QS-speed. But when it rendering 1080p50-Videos the setting with QS-Speed doesn’t work and bring an Error. For this Framerate only works the QS-quality-setting.
Sorry for my english skill too.
Best wishes!