Is it common for CQ to be slow on some and fast on others?

[InorganicMatter]

While deciding on a codec and compression rate to use on my TV shows, I experimented with a 1-minute clip. Eventually I decided on WVC1 for Xbox extending and Zune compatibility, and used AutoMKV for converting. Anyways, the clip I was playing with would get an 0.85x rate when converting at 85% quality. I moved to another clip, same setting, and it's plodding away at 0.35x! Is that normal?

[InorganicMatter]

I should have mentioned that the "fast" clip is in color, and the "slow" clip is black-and-white.

[burfadel]

depends on the complexity of the picture being encoded. What may look less complex may actually be more complex!