Cards meeting the 4.0 standard may help transferring data from a card reader to your computer, but AFAIK no current camera can write to the card at 4.0 speeds - they fit and work fine, but you don't get the 4.0 speeds. That may just mean a firmware update, but as of today a 4.0 card won't help the camera so there is no rush. Plus, the peak power consumption allowed by the 4.0 standard is higher, so overheating small cameras will be a bigger problem than it is now. Some manufacturers are advertising card controlled "thermal throttling" for 4.0 cards - as the card gets hot it slows down - rather than camera-controlled throttling as at present.
