The Vision does't appear to do any more than 1080 30p/30i, so wouldn't be as demanding as that of the Hero3 which does 60p and protune (twice the data speed). So imagine it might do ok with only Class 6.
But I'd still probably recommend getting Class 10 if you can, who knows what the future entails.
*and Class 10 cards also read faster, = faster transfers to your computer.
I often transcode my GoPro footage straight from the miniSD card.
.. imagine the same might apply to Vision footage. (tho also wonder if you can connect the Vision right up to a computer network via wifi??)