There is no class 8, just 4/6/10. It means the minimum speed for both read and write for the card.
To be honest, a class 4/6 would more than suffice, a class 10 is for HDV recording, imagine the amount of data going through.. But most people would overkill and not all are power users that will use the class 10 bandwidth fully, much less UHS-I.
It's a bit like buying a Lamborghini for SG roads, you never really hit vmax 95% of the time. My last word is, if you feel the extra money is nothing, then overkill away. Even if you watch HD videos, a class 4 read speed will suffice, my own class 4 read goes at like what, 12mbps? It's just the copying to the card that is slow, around 5-6mbps? My class 4 goes at 11.3mbps write so all's good. But I do notice the higher the capacity the slower the speed.. 32gb goes at 11 for write, and its a class 10.