It depends on the format and bitrates the videos are encoded with. The V wants H264 MP4 video, and shoots camcorder video at a rate of 2000kbps. Unless you are encoding at a very high bitrate beyond the capability of the Class 2 card, or are using an incompatible format, you shouldn't have issues.
I have a 32GB Sandisk Class 2 card and am encoding H264 video at 512kbps video and 64kbps AAC video with decent looking video playback and not-too-huge file sizes. The native video is 480x320 for the V...if your videos are sized differently and you're asking the phone to resize them, it will also degrade playback.