I doubt you will see much difference when shooting still photos. Is it worth the difference? I guess that would depend on how much the difference is. What are we talking about in dollars and cents and what size cards, what brand?
As far as a CF and SD card database, robgalbraith.com has some actual stopwatch-timed and counted RAW write time data for cameras and popular cards...but the data is old now, but still, his CF and SD card database information can show you some popular camera models which might give you an idea of how various card-classes perform. I would pick a comparable-class camera, and look at how the BEST cards performed, and also how the cheapest cards performed.
Many people feel that shooting high-definition video is a more-demanding activity on the card's performance level than is shooting RAW still photos.