@Luffy,
When it comes to Kobo touch-related things whilst reading a book, you'll get a smoother, faster response if you're reading a kepub rather than a standard epub. This includes normal page turns and highlighting/annotations.
I often read in this forum that, with recent Kobo firmware versions, standard epubs are "faster than they used to be". That may well be true but there is still a clear difference IMO.
In addition a fairly new Kobo feature is "Quick Page Turns" which lets you zip through pages by pressing and holding in the bottom corners. This is only available for kepubs.
If you've still got your H2O you could test it out for yourself with the latest firmware without needing to buy a new ClaraHD. Also, I think the Clara may have a faster processor than the H2O but don't quote me on that. Technical specs are not my forte.
