Chris i believe we will see faster write times. Which would be very handy on the M8 the buffer is good but does not win races either. I think SDHC will improve performance plus i think better security on the card.
i found this on a site just now
SDHC (Secure Digital High-Capacity) cards are flash memory cards with a minimum capacity of 4GB (gigabytes). SDHC cards provide removable memory for compatible digital devices including cameras, camcorders, PDAs, MP3 players and more. Secure Digital refers to a specific format within the flash card market. SDHC cards are designed for devices that are compatible with the SDHC 2.00 specification. Products designed exclusively to support previous SD specifications 1.0 and 1.1 will not be able to utilize SDHC cards.
The growing demand for high-capacity flash memory springs partially from the increasing use of high-definition video and high-resolution digital photography. SDHC cards meet the challenge of these demanding products not only by providing ample storage but also by introducing a new feature: classifications of data transfer speed (DTS). Consumers can get the best performance value out of their digital products by using flash memory cards that support the device's highest standards for data transfer speed. The SDHC specification 2.00 calls for cards to be classified according to the minimal sustained DTS as follows:
Class 2: minimum sustained DTS of 2MB/sec
Class 4: minimum sustained DTS of 4MB/sec
Class 6: minimum sustained DTS of 6MB/sec
SDHC cards are classified to guarantee a specific sustained DTS. This potentially saves consumers money, as flash cards are priced not only according to capacity, but also to speed. For example, if a product's maximum DTS is 2MB/sec, dishing out extra cash for Class 4 or Class 6 SDHC cards would be a waste of money. Conversely, devices that can utilize the 4MB/sec or 6MB/sec DTR will perform significantly better with Class 4 or Class 6 SDHC cards, respectively.
http://www.wisegeek.com/what-are-sdhc-cards.htm